Move add_to_class functions to their own module

* The new module is called methods.py and found on each app.
* Add keyword arguments to add_to_class instances.
* Remove catch all exception handling for the check in and
  check out views.
* Improve checkouts tests code reducing redundant code.

Signed-off-by: Roberto Rosario <roberto.rosario.gonzalez@gmail.com>

mayan/apps/cabinets/widgets.py

@@ -43,7 +43,7 @@ def widget_document_cabinets(document, user):
     )
 
     cabinets = AccessControlList.objects.filter_by_access(
-        permission_cabinet_view, user, queryset=document.document_cabinets().all()
+        permission_cabinet_view, user, queryset=document.document_cabinets()
     )
 
     return format_html_join(