Add new Calendar APIs to fw

b/5317399 b/5309787 b/5207781 b/5347210 Adds apis for a color
table to support future migrations. Adds allowedAttendeeTypes
and allowedAvailabilities for exchange/gsync support. Adds
type_resource for attendees and tentative availability. Documents
that eventTimezone is required for creating an event.

Change-Id: Id3f866c46f76f2b5b098f4961ea09d48f17598c3