[2.0][DC-460] Refactored cache bulk deletion methods to use driver specific features to retrieve list of keys. Also, refactored tests
so that all methods are tested for all drivers.

Removed:

- Doctrine\Common\Cache\AbstractCache::count()
- Doctrine\Common\Cache\AbstractCache::deleteAll()

API Changes:

- Doctrine\ORM\AbstractQuery::getResultCacheId() now public

Bugs fixed:

- Doctrine\Common\Cache\AbstractCache::deleteByPrefix() was deleting _every_ key in cache

[2.0] Small refactorings on the cache drivers. Introduced flag to control whether the cache driver should manage the cache keys since this is an advanced feature that is not always needed and can have negative side-effects (higher probability for cache slams).

[2.0][DDC-48][DDC-47] Refactored cache drivers to allow more control over deleting, added namespacing to cache drivers and implemented clear-cache task