Tie Kolab_Storage to Horde_History if enabled

Otherwise Kolab_Storage_Factory::createHistory()
will use the in-memory only Horde_History_Mock object.
Fix Kolab <-> Horde_History sync marker: The 'sync' timestamp must be per folder

Otherwise one folder overwrites the sync marker of other folders.

We need to keep our own timestamp since the sync of a folder cache
might be successful but the history sync could fail (timeout etc).