MacGui: Peak Framerate initial implementation

MacGui: Peak Framerate initial implementation
- Adds a checkbox below the fps drop down to allow selecting pfr as long as Same as Source is not selected.
- Checkbox is shows and hides based on the fps dropdown.
- Uses job->cfr = 2 instead of 1 to enable libhb's pfr mode.

git-svn-id: svn://localhost/HandBrake/trunk@3390 b64f7644-9d1e-0410-96f1-a4d463321fa5