Closes #177

Closes #194

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.