GFX now handles non-default adapters

The GFX (DirectX) pipeline did not respect the choice of adapter and
always went for the default one.  Normally this isn't an issue unless
you wish to target a particular adapter and display device combination.
This has been corrected.

The GFX initialize functions now attempt to find the best adapter that
matches a given display device (i.e. monitor) if one has been passed in.
To aid with choosing a display device some new monitor enumeration
methods have been added to the platform window manager.  These methods
have been exposed to the Canvas.
Merge pull request #318 from DavidWyand-GG/GraphicsAdapters

GFX now handles non-default adapters