Issues on High DPI Displays (e.g. Retina)

Some tutorials are not rendered correctly on High DPI displays, since these displays were not supported in the original project. Examples of what should be changed to fix this:
- `gl_FragCoord.y / 500.0f` in `src/integeruser/jgltut/tut02/data/FragPosition.frag`
- `persMatrix.scale(2.0f / w, -2.0f / h, 1.0f);` in `src/integeruser/jgltut/tut16/GammaRamp.java`