Closes: #188

BREAKING CHANGE:

feat: use Django model permissions for Category, FundingCategory, Language, License, LinkType, MusicFocus, Topic annd Type

Closes: 183

remove TimeSlotManager and use them as functions

The dashboard will need to implement a paginated list of shows
that should be searchable.

In aa7e7f41 filters were renamed
to a camelCase scheme. This is actually wrong, because the filter
names are already transformed to snake_case when the are applied
to the FilterSet.

We need the search filter to implement a user complete field in the
dashboard.

The Timeslot no longer has a show attribute. It is exposed through timeslot.schedule.show instead.

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

Closes: #167

Closes: #171

Closes #152

Closes #152

To be honest I'm not sure this is the right way to do it.

The seralizers for Host, Note and Show require the request in the
context, but only the `APINoteViewSet` calls `get_serializer_context`.
The other two `APIHostViewSet` and `ShowSerializer` ingnore it, and the
request needs to be added manually.

- The user or username is no longer "injected" in the view sets
- The user and username are obtained in the serializers from requests