window: Atomically unmaximize both directions from a _NET_WM_STATE ClientMessage

When GDK sends an unmaximize _NET_WM_STATE ClientMessage, it tells us to remove
the _NET_WM_STATE_MAXIMIZED_HORZ and _NET_WM_STATE_MAXIMIZED_VERT states. Before
this time, it would independently call:

  meta_window_unmaximize (window, META_MAXIMIZE_HORIZONTAL);
  meta_window_unmaximize (window, META_MAXIMIZE_VERTICAL);

Which, besides being foolishly inefficient, would also mess up our saved_rect
tracking, causing the window to only look like it was unmaximized vertically.

Make this code more intelligent, so it causes us to unmaximize in one call.

https://bugzilla.gnome.org/show_bug.cgi?id=722108
monitor: improve heuristic to determine display output name

Under some circumstances, for example when the display controller driver
doesn't report back the correct EDID, or under VirtualBox, Mutter
returns suboptimal strings for an output display name, leading to funny
labels like 'Unknown 0"', or '(null) 0"' in the Settings panel.

This commit improves our heuristic in three ways:
- we now avoid putting inches in the display name if either dimension is
  zero
- we use the vendor name in case we're not able to lookup its PnP id
  from the database. Previously we would have passed over '(null)'
- as a special edge-case, when neither inches nor vendor are known, we
  use the string 'Unknown Display'

Finally, we make the combined vendor + inches string translatable, as
different languages might want to move the size part of the string to a
position different than the end.

https://bugzilla.gnome.org/show_bug.cgi?id=721674
monitor: Suppress -Werror=unused-variable

Fallout from 477acddf642d735ef036a95fda6f4d7f6b522fd1

https://bugzilla.gnome.org/show_bug.cgi?id=721674
Changed obsolete FSF postal address into generic URL.
Fix https://bugzilla.gnome.org/show_bug.cgi?id=721517 #2
Updated obsolete FSF postal address in COPYING
Fixed https://bugzilla.gnome.org/show_bug.cgi?id=721517 #1