Add filter for 'backend' to user REST route

This adds a "backend" type filter to the index REST route which is a pre-requisite for https://github.com/owncloud/core/issues/12620

For example when calling `index.php/settings/users/users?offset=0&limit=10&gid=&pattern=&backend=OC_User_Database` only users within the backend `OC_User_Database` would be shown. (requires sending a CSRF token as well)

Depends upon https://github.com/owncloud/core/pull/12711
introduce inApps[] filter for search via ajax query, make file results show up in files app only

use more flexible return type

check array with !empty instead of count
Add login/logout to TestCase base class
adding dependencies for command line tools
adding supported libraries - including min and max version
adding dependencies for supported platforms
adding dependency to owncloud version - with fallback to requiremin and requiremax
Add user parameter to tag manager
Break loop
Use public interface
adjust styling of missing dependencies in apps management
single dependencies will not be represented as an array + fix unit tests
fix unit tests
check app dependencies on installation as well
Added searchByTags to view, storage and cache
Move file thumbnail into the label element
Replace input checkbox CSS selector with .electCheckBox
Make $userId mandatory for searchByTags

$userId is now a mandatory parameter for searchByTags.

Also fixed some places in the code where the argument was missing (Node
API and View)
Added searchByTag in cache jail wrapper
rework api of DependencyAnalyzer