Paging:  Make callers monitor-context aware

When switching pages/desks, don't assume the desk/page in question is the
monitor which has the mouse pointer.  It's entirely possible the context for
the monitor are from the window (as in a ClientMessage, for instance).

Therfore, make all places where switching pages/desks happens to pass in a
struct monitor *, and use that.
ActiveWindow:  Force a goto_desk()

When receiving a _NET_ACTIVE_WINDOW message, also ensure the appropriate
desk is selected.  This might still happen with additional commands from
EwmhActiveateWindowFunc (such as WarpToWindow), but this should happen by
default.
WarpToWindow:  Don't check monitor boundaries

When trying to warp to the specified window, the old code used to look for
the screen-boundary edges, and if the window was over them, move the window
into place.

With separate monitors, this isn't needed, so ignore it.
Remove debug messages

These are no longer needed.