Refactor template assignment of top menu + isFileWritable()

core/Controller/Admin.php

plugins/CoreAdminHome/Controller.php

plugins/CorePluginsAdmin/Controller.php

plugins/CorePluginsAdmin/templates/plugins.twig

plugins/DBStats/Controller.php

plugins/Installation/Controller.php

plugins/MobileMessaging/Controller.php

plugins/PleineLune/PleineLune.php

plugins/PrivacyManager/Controller.php

plugins/SecurityInfo/Controller.php

plugins/SitesManager/Controller.php

plugins/UserCountry/Controller.php

plugins/UsersManager/Controller.php

plugins/VisitorGenerator/Controller.php