feat DAV and skill rework

[emphasize]

First and foremost it's a about DAV intergration to sync alerts with a DAV server (tested with nextcloud), but comes with a multitude of improvements to make the skill a viable organizer

• apart from the usual types (alarm, reminder, timer), added:
  • todos/tasks (aka. VTODO)
  • todo lists (organize todos in list form; eg shoppping list)
  • events (differentiation between reminder/event: length; better organisation due to overlap check)
• extended input disambiguation as a combination of fuzzy matching and user reaffirmation
• change alert properties (rather than create anew)
• reschedule all different types
• extended snooze mechanic
• media player interface
• GUI (alert) list display
• own converse management

I guess it will be come down to a review by live testing, but things in particular to hash out/check for futureproofing are

• session integration (session persists in the alerts' context)
• OAuth integration (to serve from google,..)

To get a first glimpse, take a look at the README.
I've tried to get as much information in there as possible (without overburden the reader)

There is a good chance that i forgot something, given the mass ...
oh, and don't worry about the unittests, they will need adjustments when all is said and done.

[builderjer]

I have not seen a dual license that is Apache and GPLv3 as in caldev. I guess that is what is failing on the license tests.
I guess the question for that would be which license would apply here?