Call notification per KleinKleeBlatt

With the add-on you can via the Fritz!Box:
- be notified and/or signaled about incoming calls.
- Display calls and phone book.
- Start calls. Also from pages by highlighting the phone number and then opening the context menu.

This add-on uses the official AVM interfaces using the TR-064 protocol.

A help page can be found in the settings.

To be notified about incoming calls, Python is required on the PC.

Currently it is still in beta phase. If there are any questions, bugs or suggestions for improvement, they can be described on the Github page or in the comments/reviews, if applicable.