Update core/ICF_Model: Officially deprecate $this->formitem
Update models of module settings to use numeric primary keys
Update core/Nested_set_Model to work with id == '1' for item "ROOT"
Update module 'acl' models to use integer primary keys
Update lib acl/Acl to use primary-key == '1' for "ROOT"
Update ctlrs of module 'acl' to work with integer primary-keys
Update model users/user to work with integer primary key (length 16)
Update file-template "model": Remove deprecated "$input"
Update migrations to:

* Integer primary keys
* Use dbforge instead of pure MySQL-queries
Update helper ICF_array

* Add function dp()
* Uses ob_buffer for dd() and dp()
Merge branch 'feature/app-cores' into develop