Add or remove permissions from groups as defined by the RuleSet links

- Only runs when the group is changed
- Does not add permissions if they already exist
- Does not remove permissions if they do not exist

InvenTree/users/tests.py

@@ -76,7 +76,6 @@ class RuleSetModelTest(TestCase):
                     print("{n} is not a valid database table".format(n=m))
                     errors += 1
 
-
         missing_models = []
 
         for model in available_tables:
@@ -89,4 +88,4 @@ class RuleSetModelTest(TestCase):
                 print("-", m)
 
         self.assertEqual(errors, 0)
-        self.assertEqual(len(missing_models), 0)
+        self.assertEqual(len(missing_models), 0)