Allow apps to add/modify config js output via hook.

core/js/config.php

@@ -62,7 +62,10 @@ $array = array(
 			'session_keepalive' => \OCP\Config::getSystemValue('session_keepalive', true)
 		)
 	)
-	);
+);
+
+// Allow hooks to modify the output values
+OC_Hook::emit('\OCP\Config', 'js', array('array' => &$array));
 
 // Echo it
 foreach ($array as  $setting => $value) {