Xtile: per area monocle.

Add an ismono flag to each area, meaning that a monocle area will show a deck of
its clients, all with the same geometry. In the case of the global area, the
implemented mechanism subsumes the monocle layout, so this layout was removed.
Merge branch 'xtile' into xtile-gaps

Conflicts:
	dwm.c
Merge branch 'xtile-gaps'
Noborder: Layout-agnostic criterion.

Determine whether a border should be shown or not considering only the client
geometry. This removes a dependency on the currently installed layouts and the
behavior of those layouts. With the new implementation any layout would get
noborder working without further effort. The "floating layout" (no layout)
and floating windows always show borders.
Merge branch 'noborder'