Implement AS 16.0 support

[nvsystems]

Recreation of bug https://jira.kopano.io/browse/ZP-713:

On the 14th of September 2015 MS published new AS documentation which has a new AS protocol version.
The changes include:

• enhanced calendar reliability
• attachments in calendar items
• syncing the drafts folder
  Announcement: http://blogs.msdn.com/b/exchangedev/archive/2015/06/08/announcing-exchange-activesync-v16.aspx

ActiveSync 16 has been supported in iOS since iOS 9.x (September 2015).

For cool things that are now possible with recent ActiveSync versions you can check:
https://grommunio.com/de/neuigkeiten/integration-von-exchange-activesync-16/

[matidau]

Thanks for raising this issue. AS 16.0/.1 support is still on the roadmap.

[matidau]

Still need to work on the other backends AS16.1 support

[matidau]

Bit more progress on AS16.1.

Still need to Finish working on the IMAP Backend and drafts.