Hardcode database name into Horde_Mongo_Client

i.e. object passed to calling data can only modify that database.
SessionHandler storage objects do not support serialization
Optimize cache set/update into single call
Build indexes for mongo db
Allow cache mongo db collection name to be configured separately
[mms] Add MongoDB token backend.
Support NoSQL drivers (mongo) for Token package
[mms] Convert unit tests to PHPUnit.