Django 1.7 support: add AppConfig
Django 1.7 support: Fix app_label and override ClearMemcacheAdmin.get_queryset()
Django 1.7 support: check for _lib atribute on the cache class

Since 1.7 a wrapper proxy class is used for caches which breaks the previous
check. Hence check for the private attribute '_lib' on the cache class which
is currently unique in Django for the memcache classes.
Still a weak check.
When checking for jQuery, also try a namespaced jQuery