Add hibernate feature to mod_muc.

The hibernate configuration enables empty persistent MUCs to be terminated.
Store and restore persistent MUC histories to muc_history table.

Add MUC configuration option 'persistent_history' which enables chat history queues
to be serialized into lists and stored in Mnesia.

Also commented out code that starts all persistent mod_muc_room processes at startup.
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Add configurable option 'load_persistent_rooms' to mod_muc

Option controls whether persistent rooms are loaded at mod_muc startup or
loaded on demand only.
Merge branch 'integrate-rumble-muc'

Integration of Rumble specific MUC changes:
+ Hibernate empty MUC rooms
+ Store persistent MUC history to Mnesia
+ Configure loading of persistent MUCs at startup
+ Supress MUC presence broadcasts to other users