Move $strings from App to Core\L10n

- Add L10n::init() call in App constructor
- Improve pushLang/popLang
- Remove no longer needed references to App

mod/register.php

@@ -63,7 +63,7 @@ function register_post(App $a)
 
 	$arr['blocked'] = $blocked;
 	$arr['verified'] = $verified;
-	$arr['language'] = L10n::getBrowserLanguage();
+	$arr['language'] = L10n::detectLanguage();
 
 	try {
 		$result = Model\User::create($arr);