Added searchByTags to view, storage and cache

Added searchByTags to view, storage and cache.

This required adding the user parameter in the tag manager as well.

Please review @LukasReschke @icewind1991 @nickvergessen 

Supersedes https://github.com/owncloud/core/pull/12617 due to Jenkinitis
No, because this is an interface method (well, there is no interface for "Cache" yet but it has to be consistent with the non-shared cache)