Add DisplayModeUtils

[crykn]

Add an utility class which offers static methods for dealing with display modes. Something like this:

• enum DisplayMode - windowed, windowed/borderless fullscreen, fullscreen
• getDisplayModes() , getSelectedDisplayMode(), setDisplayMode(...)
• getResolutions(), getSelectedResolution(), setSelectedResolution(...)
• isVsync(), setVsync()
• Monitor, AspectRatio, etc.