feat(xmonad): replace Full layout with simpleTabbed
feat(xmonad): replace Full layout with simpleTabbed

simpleTabbed is basically like the Full layout but with a tab bar at the
top. I original kept Full layout there before because I thought the
`mkToggle (single NBFULL)` part needed it, but now I realise that that
is not the case.

vyp/ui,vyp/etsi