Close #51

- Make `Host.is_editable`, `Show.is_editable`, `Note.is_editable`, and
  `Note.get_audio_url` static methods,
- Make `Schedule.instantiate_upcoming`, `Schedule.generate_timeslots`,
  `Schedule.get_collisions`, `Schedule.generate_conflicts`,
  `Schedule.make_conflicts` and `Schedule.resolve_conflicts` static
  methods. Most of these methods do not belong here.
- Fix signatures of methods for subclasses of `viewsets.ModelViewSet`
- Fix doctrins for subclasses of `viewsets.ModelViewSet`
- Fix comparisons with None (replace '==' and '!=' with 'is' and 'is not')

Also clean-up unused imports.

- Field "FundingCategory" is not mandatory anymore
- Added new field "is_active": Active shows will be determined either by existing timeslots in the future (if show is active). If show is not active it will always be considered as inactive, even if there are upcoming timeslots.

+
* Fixed bug when deleting a note
* Extended schedule list view and filters in admin ui
* Got rid of unnecessary scopes
* Rearranged settings

* for adding a number of (business) days to the schedule (e.g. "on the rrules' following day")
* fixed a bug for monthly recurrences
* and some minor changes

See #8

* added corsheaders middleware to work properly
* fixed bug when updating a timeslot
* after updating a timeslot, its repetition will be returned if there's one
* included field 'ppoi' in shows

See #22 #23

See #21 #23

and:
* Set correct login redirect url for oidc
* Added django-cors-headers for cross-domain api requests

See #21 #22

* Properly generate thumbnails for shows, hosts and notes
* Return thumbnails in API

See #22

...as well as some minor changes and bug fixes.

See #8 #10 #22 #24

...and filters for admin ui and api.

See #21

* Added dryrun
* Added reassignment of notes and playlists

See #8

See #8 #10 #20 #22

Documentation: https://gitlab.servus.at/autoradio/meta/blob/master/conflict-resolution.md

* Users can see and change all notes and hosts of shows they own - even if they were created by another show owner
* A host can be assigned to a note (if host is editable)
* Added django-oidc-provider app
* Added limit/offset pagination to endpoints /shows, /timeslots and /notes
* Common users may not change the show's name anymore via API
* Playout API can be called with start (date) and end (date) parameters
* Added filters to endpoints:

/shows/?host=1  Retrieves shows of a given host
/shows/?owner=1 Retrieves shows of a given owner (= user ID)
/notes/?host=1  Retrieves notes assigned to a host
/notes/?owner=1 Retrieves notes a user has created (= user ID)

Had to set settings const USE_TZ (= reflect timezone in mysql datetimes) to True for OIDC to work with mysql.

Don't know yet if that's a problem.

See #22 #23

See #21

/api/v1/shows/
/api/v1/shows/?active=true
/api/v1/shows/1/
/api/v1/shows/1/schedules
/api/v1/shows/1/schedules/1
/api/v1/shows/1/schedules/1/timeslots
/api/v1/shows/1/schedules/1/timeslots/1/
/api/v1/shows/1/schedules/1/timeslots/1/notes
/api/v1/shows/1/schedules/1/timeslots/1/notes/1
/api/v1/shows/1/notes
/api/v1/shows/1/notes/1
/api/v1/shows/1/timeslots
/api/v1/shows/1/timeslots/1
/api/v1/shows/1/timeslots/1/notes
/api/v1/shows/1/timeslots/1/notes/1

On every /timeslot endpoint, filter variables ?start=2017-01-01&end=2017-12-31 are available.

Properly create, update and delete:

* Users
  - only superusers may create
  - common users can only retrieve/update themselves
  - update is constrained to certain non-crucial fields for non-superusers

* Shows
  - only superusers may create
  - update is constrained to certain fields for non-superusers

* Notes
  - creating/updating is constrained to shows and timeslots the non-superuser owns

* Schedules
  - only superusers may add/update/delete
  - collision detection still needed

* Timeslots
  - direct creation is prohibited for everyone (only by adding/updating schedules)
  - update is constrained to certain fields
  - only superusers may delete


Available GET endpoints for (only superusers may add/update/delete)

* Hosts
* Types
* Topics
* Categories
* RTRCategories
* Languages


See #22 #23

Problem to solve: there's a mix between API usecases for Playlist-UI and Website.

See #22

Shall we still put this in a sub app?
Would still need to figure out how to hook from the sub app into the serializer viewsets (and not vice versa) in order the custom fields get saved.

See #21

Extended Category model with color and description.
Extended Note model with field audio_url, to be able to playback audio files directly in the mobile app.
The field is hidden and will only be used to automatically retrieve the direct file's URL from CBA if the settings variable CBA_API_KEY is set and valid.

See #24

Updating is constrained to defined fields.
See #22

Implemented django-oauth-toolkit for authentication.

Working on prototype for playout API (momentarily still called week_schedule())

Added permission restrictions for common users in APIs
See #23

Added playlist_id to TimeSlot datamodel
See #21

Made some minor changes in calendar.

See #23

- Let them only edit their own user profile and only certain fields
- Let them only edit shows they own and only certain fields
- Let them only edit own notes and only assign them to shows and timeslots they own

Removed some unused code and added some help texts to form fields.

* Improved note selection: Users choose their shows and corresponding timeslots are loaded into the select via ajax (improvement still necessary to avoid queryset when initially loading)
See #17

* Users can only see and edit their shows, timeslots and notes
* Users can only edit their own profiles

* Changed fallback_playlist to fallback_playlist_id
* Timelots inherit the is_repetition flag from their schedules when created
* Added field 'memo' to timeslots (for internal notes)
See #21

See #21