module-settings: remove 'settings.persistent' option

This patch removes the 'settings.persistent' option from the configuration as it only allowed making settings persistent globally instead of individually. This issue has been addressed in a simpler way by creating a 'persistent-sm-settings' metadata. If a user wants to make a setting persistent, he can change the 'persistent-sm-settings' metadata object, if the user does not want to make a persistent change, he can use the 'sm-settings' metadata object. Any changes in the 'persistent-sm-settings' metadata will be also reflected in the 'sm-settings' metadata object.