[WIP] Default app fix

:construction:

Adds back the defaultapp setting with some extras.
Since it's now possible to disable apps for some groups, we need fallbacks.

It is now possible to specify multiple apps separated by commas.

Note that the current code doesn't work for all apps.

For some reason the "contacts" app is giving the wrong route, needs research.
We need a better way for creating the route.

@LukasReschke @bantu @icewind1991