OGM-617 "Cache per table" strategy for Ehcache

@emmanuelbernard, @alexsnaps: Could you check this one out?

Alex, this is the new persistence strategy I mentioned yesterday. By default, we now use a specific cache per table. One can go back to the other strategy via a configuration option. Caches can be configured indvidually, as a fallback the configuration from ENTITIES, ASSOCIATIONS and IDENTIFIERS are used as a basis.
I _think_ you can ignore this statement, if I read this right, this is only called on initialization, right? I guess this is here to create missing caches from the initial config as well, y?