DATAREDIS-246 - RedisCacheManager.getCache() does not match the logical of CompositeCacheManager.

Like other `CacheManager` implementations, such as `EhCacheManager` or `JCacheCacheManager`, the `RedisCacheManager` asserts to always return a `Cache`. Therefor a new `RedisCache` is created and registered when the requested one could not be found. Up to those caches did not get registered properly and did not show up in collection of cache names.

We changed the implementation so it  makes use of `AbstractTransactionalCache` (introduced in Spring 3.2) which properly registers caches. Additionally the `loadRemoteCachesOnStartup` switch allows to retrieve and initialize existing caches by loading keys form redis server.