Suport the CalDAV `MOVE` operation

[tasn]

This is what you get when trying to do a MOVE at the moment:

Traceback (most recent call last):
  File "radicale/app/__init__.py", line 127, in __call__
  File "radicale/app/__init__.py", line 295, in _handle_request
  File "radicale/app/move.py", line 84, in do_MOVE
  File "etesync_dav/radicale/storage.py", line 576, in move
NotImplementedError

We can probably implement it internally as a create followed by deleting the original. We should just change the href if the source and destination collection are the same.

[solarkraft]

Lack of support for this makes organizing my events way more painful than it would need to be.

My workaround (in Calendar.app) is:

• Move
• Get server error
• cmd+X event
• cmd+V event

Imagine my frustration before I found out that this is the issue! Constant server errors and events disappearing. I originally thought the calendar app would implement this as a delete+create, but oh well, apparently the spec has a move event ... that ete sync doesn't support :L

[solarkraft]

Let me add to my workaround:

• Do a full reload
• Remove the event that re-appeared in the old calendar

What a pain!

Edit: But only sometimes. Have I mentioned how frustrating this is?

Edit: Stuff keeps reappearing WAY after I edited it with this frustrating workaround. By the way, it's frustrating!