OGM-228 Integration between MassIndexer and OGM

Hi,
thanks to @Sanne help I've been able to fix the infinispan issue.
This patch integrates the search MassIndexer with OGM; it makes
EntityMetadaKey Serializable; it includes OGM-273 and OGM-151.

I've added to OGM-151 some minor space fixes (that's the only change form the original pull request).

I'm using a snapshot version of search because the feature that allows the use of a custom MassIndexer has not been released yet.

Cheers