Add Message(String,String)
s/intercepter/interceptor/ in comment of EntityCapsManager
Remove obsolete comment from CapsExtension
Introduce CapsVersionAndHash

Entity Capability versions are useless without the information which
hash algorithm was used to calculate those. Right now, only 'sha-1' is
used, but this may change in the feature. This commit makes the first
steps preparing for such a feature.

Also fixes a minor bug:

-        CAPS_CACHE.put(currentCapsVersion, discoverInfo);

currentCapsVersion is not a valid key for the cache, as it does cache
"node + '#' + ver" to disco infos.
Consider also unavailable presences when dealing with the roster

This is needed for checking <delay/> extensions in unavailable
presence stanzas.

Signed-off-by: Daniele Ricci <daniele.athome@gmail.com>