[Davmail-users] Add device code authenticator

[Dick M. <di...@mr...>]

Hi!

I've implemented a device code authenticator for davmail.

Device code authentication is a bit different from call back
authentication as for device code authentication a (short) code has
to be copied from davmail to the web browser.

The advantages of this are a slightly better user experience and some
appid's don't allow/support call back authentication.

I think davmail could be refactored a bit to make these changes a bit
more clean (make the call back url optional, make a resource a single
definition, move json parsing)

Please let me know what you think of this.

Kind regards,
Dick Marinus