DATAMONGO-676 - SimpleMongoRepository now consistently uses EntityInformation.

SimpleMongoRepository.findOne(…) & ….delete(…) now use entityInformation.getCollectionName() to resolve the collection name to interact with. This allows global customizations of the collection name on repositories.
DATAMONGO-680, DATAMONGO-681 - Expose MongoOperations.exists(…).

We're now exposing dedicated exists(…) methods on MongoOperations which simply looks up a cursor and inspects it for the presence of at least one element. SimpleMongoRepository implementation now also uses this optimized exists check.