Added kColorConversion601FullRange  conversion table for Still Images

As referenced by the [comment on the pull request #1449](https://github.com/BradLarson/GPUImage/pull/1449#issuecomment-38092674), we have added an extra color conversion table for Still Images, called kColorConversion601FullRange (reference [here](http://www.equasys.de/colorconversion.html)).