Add more messages for the Ceph protocol.

New messages:
- Mon Paxos.
- Mon Global ID.
- Mon Get Version
- OSD Ping
- Ping
- OSD Boot
- OSD PG Create.
- PG Stats.

Other updates:
- Documentation for modifying the dissector.
- Update assertions to show values.
- Replace proto_tree_add_text()/expert_add_info...() by proto_tree_add_expert...().
- Fix a bug: misplaced break.
- Do some minor whitespace & other cosmetic changes.
Change-Id: Ib19ce509b67fb5e6fb31e82b5a551a9e952a9c6d
Reviewed-on: https://code.wireshark.org/review/3623
Petri-Dish: Bill Meier <wmeier@newsguy.com>
Reviewed-by: Bill Meier <wmeier@newsguy.com>