fixes #100

refs #102

This adds proper labels and description for what is happening.

fixes #193

Up until now the dashboard used a hardcoded list of rrules that matched
a long-gone fixture set of rrules in steering. Additionally, rrules were
translated in the dashboard using the the ID of the rrules in steering.
This means that any change to the fixture set, removing an rrule or not
importing the fixture set at all would mix up the translations and
therefore the actual schedules that people would create.

A few months ago the rrules were reworked and an API endpoint was
introduced that exposes the rrules defined in steering. No appropriate
change was made in the dashboard and so the rrule definitions got
out-of-sync.

This change implements a rrule store that fetches data from the API.
Additionally we’ve also implemented a custom rrule to natural language
mechanism [1]. This is because the scope of the rulesets we use in the
AURA radio context is well-known and not to complex and because rrule.js
built-in `toText` function, which might have been an option, is limited:

* bysetpos seems to be entirely unsupported
* internationalization will produce gramatically questionable
  output for languages like German, because the translation
  interface is somewhat lacking.

[1] #226 (comment 13669)

fixes #217

fixes #189

refs #127

fixes #199

fixes #210

fixes #209

This component will help us to outline areas in the dashboard app, that
are scheduled for major overhauls. This should make feedback more
effective as people testing the dashboard can focus their time & effort
on areas that haven’t received the love they deserve.

This refactor includes a bulk of the changes discussed in #181. It
removes the existing navbar and replaces it with a sidebar instead. This
leaves us more room for context-aware navigation options and other
information that is relevant to users.

Additionally, the show management page is now split up into two, the
show episodes management, listing the coming shows/timeslots and the
show’s schedules, and the show basic data page, that contains all mostly
static data for a show and which is usually maintained by
administrators.

refs #181

This change implements a show overview page with two display modes:
table and grid. Shows can be ordered and searched. Other filters are not
(yet) implemented.

refs #101
refs #181

refs #179

refs #185

refs #181

refs #146

refs #146

refs #121

refs #155 #156

Submitting a note would sometimes fail but user’s were not informed that
something went wrong, because errors not mapped to any form fields were
not displayed.

closes #137

closes #141

This can be used in views to parse the error state from steering
responses.

closes #139

refs #89