Transition from advanced_help to docs URLs #5368

#5368

#### Changes

* Remove drush.inc, help.ini files, etc.
* Remove advanced_help module from dependencies & make file.
* Add update hook to disable advanced_help.
* Move help-lookup function to an include file.
* Unify help-lookup for paths, apps, and widgets.
* Use theme_link(), not advanced_help_link for links.