Use DisplayDevice isHeadless for registering systems

Use DisplayDevice isHeadless for registering systems

Rename Display to DisplayDevice

Move opengl from StateInGame to DisplayDevice

Remove resizeViewport() and wasResized() and fold them into calling lwjgl classes

This one will cause conflicts just because the same areas of TerasologyEngine and LwjglGraphics had additional code added to them.   Both sections of code should be included in each case.
Verify DisplayDevice is registered