SAK-21497 Updated BaseCalendarService to use injection.

UsageSessionService was still using the cover, now it's being injected by Spring.

git-svn-id: https://source.sakaiproject.org/svn/calendar/branches/SAK-21497@133052 66ffb92e-73f9-0310-93c1-f5514f145a0a
SAK-21497 Added JavaDoc to new API interfaces.

git-svn-id: https://source.sakaiproject.org/svn/calendar/branches/SAK-21497@133054 66ffb92e-73f9-0310-93c1-f5514f145a0a