refs #352

refs tank#86

refs #320

We usually directly use media.entries for accessing the media sources.
This entails that these media sources are not in the media source store
because only objects that have directly been requested are stored there.

We therefore need to handle events that only contain the id.

see: #324 (comment 21200)

refs #324

refs #324

refs #324

refs #285
refs #324
refs #333

We need to wait for the timeslot to be updated before routing to the
editor page, because otherwise the editor page might redirect back to
the overview because it can’t find the episode for the timeslot.

refs #334

The show selector no longer influences the application state.

The dashboard tries to adhere to browser standards where they have
emerged. The headless ui menu was unmaintained, had some quirks and we
can now offer the same functionality with less code and based on the
popover standard.

refs #341

The selected show was stored in the browser’s local storage. This was a
remnant of the time where the selected show was a global state on which
all pages operated.

The selected show is now only stored in the current tab/window state so
multiple dashboard tabs/windows should work without issue.

refs #309

refs #332

refs #115

This changes enables us to catch typos as well as missing or updated
steering permissions in the dashboard code.

This refactoring includes some fixes, new features,
and updates to the API:

* the new /media and /media-sources APIs are used
* users can now cancel the addition of new media sources
* all errors should now be catched and displayed, no matter when
  in the handling process they happen
* users can show the import logs for uploads
* uploads happen in the background so users can move to
  other pages without aborting the upload

refs #347
refs #328
refs #323
refs #342
refs #273

refs #343

refs #343