OGM-452: Implementing "cache per table" strategy for ISPN

I still need to add a section to the documentation but aparat from that it's nearly good. Feedback welcome!
Not important but  I would have moved this selection in the `PersistenceStrategy` class, so that here you would have something like:
```
persistenceStrategy = PersistenceStrategy.getStrategy(
    externalCacheManager,
    config.getConfigurationUrl(),
    jtaPlatform,
    factory
);
```