This was an annoying remanent from DAVDroid. Maybe it makes sense for
DAV, but it defo doesn't make sense for us where we can just create
collections (and anyhow always have existing defaults!).
This adds support for tasks via OpenTasks.
https://github.com/dmfs/opentasks
Need the OpenTasks client for it to be used.
Currently you can't create new task lists. You can only have the default
one, but that's just a UI thing.
Fixes#7
This is a monster commit because to be honest, it's a monster change. It
was impossible to do it in smaller steps because things just wouldn't
compile.
We couldn't do the migration step by step because they moved to Kotlin
which was causing a lot of troubles.
Now we are all on Kotlin, so things should hopefully work just fine.
