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.