Settings: Add support for post edit callbacks

Settings can be provided with a function via the new
"post_edit_function" argument. This function will be called
when the setting's value is updated. The function will only
receive one argument: The instance of the setting being
changed.

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

mayan/apps/smart_settings/classes.py

@@ -146,13 +146,14 @@ class Setting(object):
                 path=settings.CONFIGURATION_LAST_GOOD_FILEPATH
             )
 
-    def __init__(self, namespace, global_name, default, help_text=None, is_path=False):
+    def __init__(self, namespace, global_name, default, help_text=None, is_path=False, post_edit_function=None):
         self.global_name = global_name
         self.default = default
         self.help_text = help_text
         self.loaded = False
         self.namespace = namespace
         self.environment_variable = False
+        self.post_edit_function = post_edit_function
         namespace._settings.append(self)
         self.__class__._registry[global_name] = self
 
@@ -204,3 +205,5 @@ class Setting(object):
         # value is in YAML format
         self.yaml = value
         self.raw_value = Setting.deserialize_value(value)
+        if self.post_edit_function:
+            self.post_edit_function(setting=self)