Closes #12246: General cleanup of utilities modules

* Clean up base modules

* Clean up forms modules

* Clean up templatetags modules

* Replace custom simplify_decimal filter with floatformat

* Misc cleanup

* Merge ReturnURLForm into ConfirmationForm

* Clean up import statements for utilities.forms

* Fix field class references in docs

netbox/utilities/mptt.py

@@ -4,6 +4,11 @@ from mptt.querysets import TreeQuerySet as TreeQuerySet_
 from django.db.models import Manager
 from .querysets import RestrictedQuerySet
 
+__all__ = (
+    'TreeManager',
+    'TreeQuerySet',
+)
+
 
 class TreeQuerySet(TreeQuerySet_, RestrictedQuerySet):
     """