MacGui: Constant Quality Slider now QP/RF based.

MacGui: Constant Quality Slider now QP/RF based.
- Constant Quality Slider now uses QP/RF values instead of the long maligned % scale.
- Nearest percentage is also shown for reference.
-- For reference, PercentRFConversion on the wiki is a table of corresponding values for the old and new scales.
- Slider changes scale base on the chosen encoder.
-- x264: 0-51
-- FFmpeg and Xvid: 1-31
-- Theora: 0-63
- x264 Specific - Slider allows for fractional granularity (other encoders just whole ints).
-- Advanced Preference to adjust the granularity from 1.0,0.50,0.33,0.25,0.20 with a default of 0.25.
- Existing presets using the % based values converted to the nearest QP/RF value (within the granularity of the slider).
-- Example: A current preset using x264 at 62% will now actually use 61.76% since the nearest RF value converted to 62% is 19.50 with the slider set to 0.25 granularity.
-- New presets created will store the QP/RF value instead of the % value.

git-svn-id: svn://localhost/HandBrake/trunk@2135 b64f7644-9d1e-0410-96f1-a4d463321fa5