DATAGRAPH-409 - Improved default transaction configuration for repositories.

Moved the default transaction configuration from CRUDRepository interface to AbstractGraphRepository to align with transaction configuration with other Spring Data Modules. Removed obsolete method re-declaration from CRUDRepository.

CRUDRepository was missing a redeclaration of delete(Serializable id) so that deletes by id didn't trigger a default transaction. This caused e.g. DATAREST-184.