core: removed root menus (i.e. global menu on top of window): root menus were not really useful as most actions doable there are doable through others widgets in Cagou. For actions without equivalent in widgets (like about screen), a new menu, more discreet, will be added soon. Kivy Garden's ContextMenu is not used anymore, so it has been removed from dependencies

^*media/
^*android/
^*libs/
^*bin/
^*service/