Note that CMS_SETUP provides locations set by default or from configuration file.
Now theme related resources can be found under site/modules/$mod_name/... or site/themes/$theme/modules/...
so only theme related resources can be overriden for now.
Renamed "layout" lib as "app_env" with APPLICATION_ENVIRONMENT interface.
applied changed to callers.
Added CMS_THEME.has_region (a_name): BOOLEAN to know if a region is declared in a defined theme.
