Adding plugin settings
Adding plugin settings

* This patch adds the plugin settings dict to the settings
  module.
* It allows for plugin specific entries to the conf, in a known
  location plugins can look for.
* It will default to an empty dict so it works with confs that
  have no plugin settings listed.

Change-Id: I5f6148e8eba9299d21ab414e90eb88a180279bc3

catalyst/stacktask