Started new branch: Using Google's protobuf for messages
First steps towards protobuf usage

Converting old-style commands to protocol buffer messages in the manual
testing tool.
message type added
Implemented manual testing tool for protobufs.
Removed protobuf C++ files; instead, added CMake rules
Fixed implementation mistake (wrong webapp side)
Two new protocol files and better CMake integration.

From the protocol compiler output, a static library is generated against
which the other programs may be linked.
Persistence protocol implementation -> protobuf
Fixed protocol and broker bugs
Fixed bug when saving a message (requesting user_locations on MSGS response)
Reworked ChattpMessage protocol message
Logging out user if NEWCHAN failed.
B2B protocol definition
Removed the ALSO_IF_CLUSTERED caching (too unreliable)
Webapp request implementation switched to protobufs.
Implemented protobufs for WebappResponses
Tiny clean-up
Some bug fixes after testing

- No deletion of completed transactions
- Wrong constructors for protocol messages
- Missing fields in manual-protobuf messages and broker messages
Migrated message-relay protocol implementation to protobuf
Better approach to sequence counters

New class SequenceCounter with three global instances;
SequenceCounter::get() atomically returns a new sequence number.