Notable changes:
 * Vue 2.6 to Vue 3 + compat migration.
 * Build system migration from vue-cli/webpack to Vite.
 * Application dependencies like bootstrap-vue, vue-router, vuex,
   or vue-toast-nofitication have been updated, if doing so was
   necessary or advisable for the Vue 3 migration.
 * Static file includes for the oidc-client in oidc_callback.html
   and oidc_callback_silentRenew.html have been removed in favor
   of automatic processing in the build system so that all assets
   are versioned and invalid cache hits are prevented.

Fixes #53 and #110.

moment is still needed as peer dependency but we should’t use it in our
own code anymore so we can remove it in the future.

We explicitly pass authorization for all requests and so no implicit
credentials need to be passed.

This reverts commit d37643bd.

This reverts commit 618bef34.

This reverts commit 4a37062d.

feat(nginx): deploy dashboard standalone

Closes #105

See merge request !12

Nginx in the Docker-container now ONLY deploys dashboard on
port 80. All configs related to other services will be moved to a
separate container. Certbot has been removed from the Dockerfile.

Fixes #105

This reverts commit 03470ca4.

Fix error code handling for scheduling API

Closes #93

See merge request !11

Allow API store consumers to use traditional flow-control

See merge request !10

Update toolchain and cleanup code

See merge request !9

The steering API returns HTTP 400 errors for general payload and 409
errors for scheduling conflicts that we didn’t handle yet.

fixes #93

A simple b-alert list wrapper that handles the standard error format
from Django REST framework.

Views may want to display a fallback message if the translation key does
not exist.

The steering API has some deprecated attribute names that we should no
longer use. These are:

  dstart → first_date
  until → last_date
  tstart → start_time
  tend → end_time
  byweekday → by_weekday

These changes in naming have also been applied to variable names,
attribute names and translatations in the dashboard code in order to
avoid confusion.

The currently prevalent API response handling is based on a callback
pattern. This has at least two major drawbacks:

1. More broadly it facilitates the use of nested callbacks, which make
   the code harder to read and clutter stack traces.
2. Our specific callback solution does not follow the traditional node
   callback pattern that looks like `function (err, data) { ... }`.
   Instead we have `callback` and `callbackCancel`, none of which are
   meant to handle actual error/exception objects.

The latter makes it hard to write code that is executed irrespective of
the specific code path, like in a try-finally clause. In practice it’s
also a violation of the separation-of-concerns design principle as it
forces error handling to happen in the store function instead of the
caller that is best suited to handle error states.

This change attempts to facilitate a gradual migration to a
Promise-based result handling by it to co-exist with the currently used
callback pattern. Callers that don’t provide any callback functions are
assumed to handle promises whereas callers that do provide callback
functions will see no change in behaviour.

This allows us to transition one API-call at a time instead of doing one
large and time-consuming refactoring.

refs #55

* replace all `var` declarations and use `const` where appropriate
* strip unnecessary temporary variables
* replace single character variable names
* replace multiline variable declarations
* simplify expressions
* replace invalid uses of parseInt

This updates the build toolchain to Vue CLI v5 and Tailwind 3.x along
with some other changes in tooling.

@tailwindcss/ui seems to be unused and has a peer dependency on
tailwind^1.0 that has been silently ignored.