Fix crash with iconification

Don't use FSCREEN_CURRENT to autoplace the icon; use FSCREEN_XYPOS.
Don't bail if XRandR isn't present

Rather than making the lack of XRandR a fatal condition, instead just
fall-through and assume a single screen is available.
+.
Permit windows to be focused on $OTHER_MONITOR

Don't inhibit EnterNotify focus just because the window (fw) is not on the
current screen.  Fixes issues with XRandR and input focus.
Permit iconified windows for $OTHER_MONITOR

Don't prematurely cull focusing iconified windows.
Move towards multiple ScreenInfo instances
Enables desks/pages to be per-screen

This augments the struct monitor instance to hold information about
pages/desks to be per-monitor.

Because of the way paging works, it's recommended that desks are used, and
setting "DesktopSize 1x1" doe now, so that no paging occurs, only Desk
switching (which internally unmaps the windows, rather than move them, which
is what paging does.)

FvwmPager is currently broken as well; it doesn't have a concept of
per-monitor windows, either.