Implement setAttendeeStatus

Summary:

• Require libcalendaring plugin
• Provide kolab_sync_data* classes with a means to log something, and not have to initialize/obtain a logger backend.
• Not all serverIds are longer than 64 characters.
  
  For example, when an event is created in Roundcube, and Outlook is to accept the invitation, the serverId will be CRC'ed but the event UID, and the CRC will be <= 64 characters.
• A first few baby-steps to getting back to the iTip, and possibly the event.

Test Plan: None

Reviewers: machniak, adomaitis

Subscribers: adomaitis, machniak

Differential Revision: https://git.kolab.org/D515