Superusers should see all shows. Ordinary users only those shows that belong to them.
Therefore we have to fetch the user data from the steering backend as well (OIDC info
alone does suffice here).

We need this info later too, when we implement user managament and profile settings.

In the ShowManager we now generate the GET URI depending on the superuser status.

still TODO regarding OIDC:
* handle token expiration and refreshing

still TODO regarding ShowManager:
* finalize all requests for ShowManagerModal*
* change getting notes: we now have a note_id in every timeslot
* handle repetitions when updateing timeslots & notes
* creation of new timeslots and collision handling

includes:
* new pretty date functions
* fetching of timeslots through getTimeslots function

now prepared for pagination, has to be implemented next

includes:
* new pretty date functions
* fetching of timeslots through getTimeslots function

now prepared for pagination, has to be implemented next

as vue-resource is retired from official recommendation status
we switch to axios, which is better maintained and supports a
similar API.

for more background see:
https://medium.com/the-vue-point/retiring-vue-resource-871a82880af4