* add cache to redis
move out cache module from mongo
* fix redis tests
* add callback noop
* fix typo
* del cache on field delete
* make redis/mongo caches separate
Groups.destroy can take an array of groupnames
Groups.leave can take an array of groupnames
db.incrObjectField/decrObjectField can take an array of keys
db.sortedSetRemove can take an array of keys and values
db.setRemove can take an array of keys
* cache mongodb objects
remove user settings cache since it is cached at the object level
* removed indexOf from isMemberOfSets
* change has to get, change maxAge to 0
new method emptydb
use emptydb instead of flushdb, flushdb removes indices for mongo which
breaks search tests
initialize meta.config properly in tests
enable nodebb-plugin-dbsearch for tests