Various fixes to PeopsOpenGL preferences UI on OSX

- Fixed frame buffer effects options
- Added frame buffer access options
- Frame limit setting was being ignored
- VSync setting was being ignored
- Texture filtering was being restrained to a 0-2 range instead of 0-6
- Scanline color picker was not being enabled properly
- Dithering is a boolean option so changed it to a checkbox
- Minor layout problem with the windowWidth field on OS X 10.10+