COMP: Adding support for Apple's Retina display for fonts

Enable improved rendering of fonts on Apple's retina displays by
adding a custom bundle plist file with the following additional
elements:

<key>NSPrincipalClass</key>
<string>NSApplication</string>
<key>NSHighResolutionCapable</key>
<string>True</string>

The remainder of the input plist file is based on the current in file
from CMake.

For reference: https://blog.qt.digia.com/blog/2013/04/25/retina-display-support-for-mac-os-ios-and-x11/

Co-authored-by: Jean-Christophe Fillion-Robin <jchris.fillionr@kitware.com>

From: Bradley Lowekamp <blowekamp@mail.nih.gov>

git-svn-id: http://svn.slicer.org/Slicer4/trunk@22870 3bd1e089-480b-0410-8dfb-8563597acbee