Start standardizing on "client" instead of "device" or "PIM".
Add support for encoded MAPI GOID fields, and simplify.
Actually, this isn't needed.
Don't ignore the client-provided UID for EAS meeting requests.

Fixes the issue where the iTip request generated by the EAS client
and the iTip responses generated by the email client were mismatched
with the UID generated by Kronolith when the event was imported.
Restrict to user-owned calendars here.

Otherwise, EVERY time an iTip is initially viewed for an event that
was created by another local user the language will show "update"
and a Permission Denied error is shown to the user before a success
message is shown.
Can't test the method return value for empty().