Closes: #187

- replace LicenseType with License model, update fixture, serializers, views, and urls

Closes: #167

Closes: 137

- `Category`,
- `FundingCategory`,
- `Language`,
- `MusicFocus`,
- `Topic`,
- `Type`

- remove `ActiveSchedulesFilter`,
- remove `ActiveShowsFilter`,
- replace `ActivityFilter` with `ActiveHostsFilter`, since it remains in use

Close #51

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

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

...and filters for admin ui and api.

See #21

* 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