Previously any entity capability lookup was only cached on the disk. This meant that even for a cache hit, you would read from disk and parse the disco info XML in the cache, to return the result. This commit adds an addition LRUCache based in-memory cache. This extends the EntityCapsProvider API with a non-const method, i.e. getCapsCached, which allows active caching of results from the disk cache. Test-Information: All unit tests pass on macOS 10.12.3. This noticeably speeds up the duration of a join of a large MUC room, i.e. about 160 occupants, to about half of the previous duration. Change-Id: I0fc254cda962860416713822ddcad15ae13085f1