Enable device filtering on desktop (bug 1054981)

https://bugzilla.mozilla.org/show_bug.cgi?id=1054981

Note: the UI to deactivate the compatibility filtering is in a different bug, [bug 969244](https://bugzilla.mozilla.org/show_bug.cgi?id=969244), but is blocked by design considerations atm. I wanted to merge filtering first because I don't think the compatibility toggle button is that important anyway (why would you want to see apps you can't install ?). If you disagree r- me :-)