Create an /etc configuration manager module

Created by: SunilMohanAdapa

Allows user to roll back and fork their /etc configuration via etckeeper.

How should Plinth refresh its configuration? On each page load? Should it cache each settings file's values based on the last modified date (akin to make)?

The Run etc-keeper --commit around each action and commit /etc Periodically

TODO items will also be included in this module when it's complete.