main: get window size from gtk

With this patch we can start wkline from wayland and the desktops widget will fail and return keeping the bar alive
main: reserve toolbar space so normal windows can't go bellow it
main: add monitor option in config.h
Merge remote-tracking branch 'ricardo-vieira/wayland' into develop
Cleanup whitespace
Merge branch 'develop' of github.com:Lokaltog/wkline into develop