Add more caching in the group manager
Delay fetching the display name until it is requested
Only check for existence of shared files when doing shared storage setup

The getItemsSharedWith function also retrieves related information,
resulting in work that isn't used here.
Clear the cached user groups when a group is deleted
Also clear cached UserGroup when a user is added/removed
Add unit tests for getUserGroups with addUser and removeUser
Use limit=1 so the db can stop searching on the first hit
Merge branch 'master' into optimize-startup-queries

Conflicts:
	apps/files_sharing/lib/sharedstorage.php
	tests/lib/group/manager.php

removed hasFilesSharedWith from lib/public/share.php and
sharedstorage.php to fix merge
Merge pull request #7363 from owncloud/optimize-startup-queries

Optimize some queries that are always executed when loading base.php