Simplify CMS_SERVICE initialization, and CMS server (launcher).

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.

src/service/response/cms_response.e

@@ -107,7 +107,7 @@ feature -- Module
 	module_assets_location (a_module: CMS_MODULE): PATH
 			-- Location for the assets associated with `a_module'.
 		do
-			Result := setup.layout.path.extended ("modules").extended (a_module.name)
+			Result := setup.environment.path.extended ("modules").extended (a_module.name)
 		end
 
 	module_assets_theme_location (a_module: CMS_MODULE): PATH