Support tower license within the database

With backwards support for the file-based license

awx/main/models/configuration.py

@@ -54,6 +54,8 @@ class TowerSettings(CreatedModifiedModel):
             converted_type = [x.strip() for x in self.value.split(',')]
         elif self.value_type == 'bool':
             converted_type = self.value in [True, "true", "True", 1, "1", "yes"]
+        elif self.value_type == 'string':
+            converted_type = self.value
         else:
             t = __builtins__[self.value_type]
             converted_type = t(self.value)