Fix Permission Cache Key Collision

Fix permission cache key collision

- Change `PermissionCache::addAccessObject()`
- Change `PermissionCache::clearAccessObject()`
- Change `PermissionCache::getAccessObject()`
- Change `pk:` cache prefix to `pk:` prefix

Collisions occur with `PermissionCache::addValidate()` as both use `pk:`
cache prefix
Merge pull request #1171 from mkly/fix_permission_cache_key_collision

Fix Permission Cache Key Collision