Since we now use a setup component for the calendar the old comments are
no longer relevant and we can use a regular slot.

refs #247

Users have a hard time selecting timeslots if the title column is empty.

refs #274 #276

Steering now creates notes for timeslots automatically.

refs #274 #276

refs #286

Now that bootstrap-vue is no longer used we can finally deactivate the
Vue 2 compatibility mode.

This is a big one because it’s hard to make these kind of changes
atomic. This changeset reworks the calendar component which is no longer
dependent on bootstrap and vuex.

As a consequence we can remove axios, bootstrap, and vuex because the
calendar was the last remaining part of the code that was still using
them.

refs #127 #140 #261 #279

This is helpful if multiple operations should use the same error object.

This makes it easier to set styles specifically for the wrapping
container.

refs #247