Some reusable refactoring into generic BackEnd possible

(still unconnected to actual MQTT in this commit!)

Recent addition of IntegerConverter in rsb0.14 seems flaky (it
seems Python will always send 64bit, and no conversion can be made),
-> now using 64bit types for transport everywhere revision numbers
are exchanged as an RPC result, i.e. all RemoteIU modifications
and ResendRequests (Also disabled our own legacy IntConverters).

Note: the ipaaca.proto Protobuf definition has not been changed,
for compatibility reasons. Java version contains explicit (int)
casts when protobuf objects are built. (TODO Discuss proto->64bit)

Tests between all three languages work (Netboot, rsb0.14,
protobuf2.6.1, spread4.4), tested with WOz+Cere+Billie.

Also re-renamed the other two back to --rsb-host and --rsb-port ;)

Use with Locker, possible in a dedicated stack frame, like this:
// ... code ...
{ // open stack frame
	Locker locker(iu->payload());
	iu->payload()["a"] = "string";
	iu->payload()["b"] = "simultaneouslySentString";
} // close stack frame, sending the update

Also renamed some functions (preserving old names as deprecated aliases)

Sniffer: only display quotes for string-type payload values
Injector: using unicode() and catching errors

TODO: compatibility with STR legacy payloads; more varied
access to inner payload objects (e.g. push_back)