Make the Menu app not seen as an AWM

Currently Menu app is accessible from Administration and is an application intended for Admins. Menu is listed in the AWM list, although it should be seen as a standalone core extension.

Discussed on IRC (13 Mar 2019):
mflorea: IMO a better fix is to simply make the Menu app not seen as an AWM.
vmassol: +1 to consider that as soon as an app is an extension it looses being an AWM app.

Also we should adapt the UI (but maybe an another issue): remove the AWM actions, make it look more like an individual extension, than an AWM.