Use separate main geometry settings for Qt and GTK+.

Use separate main geometry settings for Qt and GTK+.

Qt and GTK+ can have wildly different notions about the top-left
position of the main window, particularly in multiple-screen
configurations. For example, on OS X with the following monitor
arrangment:

  g         .---------.
            |         |
            |         |
  q--------.|         |
  |        |`---------'
  |        |
  `--------'

GTK+ positions windows relative to 'g' and Qt positions windows relative
to 'q'. As a result it's easy for one UI to clobber the settings of the
other.

Split the geometry_main_x and geometry_main_y recent settings into Qt
and GTK+ versions.

In the Qt UI, try moving the main window onscreen before falling back to
the default geometry. This keeps us from losing our size settings.

Add a link to a Qt geometry bug.

Change-Id: If7ae0dcc1719e646299ee3bbf1c88743f655c9a0
Ping-Bug: 12389
Reviewed-on: https://code.wireshark.org/review/15775
Reviewed-by: Gerald Combs <gerald@wireshark.org>
Petri-Dish: Gerald Combs <gerald@wireshark.org>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Anders Broman <a.broman58@gmail.com>