Add acl/acl_helper to module acl

Currently there is only one function implemented 'acl_allowed' to check if access to certain resources is allowed or not
Add ctlr and views for 'admin/acl'
Add routes for 'admin/acl/{roles,resources,permissions}
Add language for module acl, part admin
Update core/Nested_set_Model::{delete,delete_tree}

Changed parameter $preserve_children to $delete_children and inverted method's logic
Add file comment header to some ACL files
Add a _before_create method to model acl/acl_role_m
Update many functions for lib acl/Acl
Update language file for acl/admin
Update lib acl/acl to use proper nested-set-model methodnames
Merge branch 'develop' into feature/acl

Conflicts:
	icf/core/Nested_set_Model.php
Update models acl/acl_{resource,resource_role,user_role}_m

Udpate to call parent::__construct() on __construct()
Merge branch 'develop' into feature/acl
Update Nested_set_Model: Add move_{after,before} methods
Update ICF_Model: Add ICF_Model::primary() to return name of primary field
Updated Nested_set_Model: Add method Nested_set_Model::_move_before_after

Is incomplete, though
Update lib acl/Acl with role-managing methods
Merge branch 'develop' into feature/acl
Merge branch 'develop' into feature/acl
Move views of module acl to themes location