Cache: CachedBehavior not deleting the correct files

This change introduce CroogoAppModel::$cacheConfig that stores the last
cache configuration name that was last used.  CachedBehavior will then use
this value in _deleteCachedFiles().  This property is not documented and
only intended for backward compatibility purpose.
Cache: Move cache config to the appropriate plugin
Merge branch '1.5-cache' into 1.5