[UPDATE] ACL Management

* [ADDED] Smarty acl_check function
* [ADDED] Optional default return  value for getValue calls
* [UPDATE] ACL Checks in page controllers
* [UPDATE] Navigation template to use check_acl from Smarty
* [ADDED] New ACL options where needed
* [REMOVED] Disable pages from System Settings Tab
* [ADDED] Above removed pages into ACL Settings Tab

This will make usage of ACLs a bit easier and transparent.
Also fixes #1731 once merged.