MacGui: Enable soft vobsubs in mp4

MacGui: Enable soft vobsubs in mp4
- Initial patch by Rodeo. Thanks Rodeo!
- Enables soft vobsubsin macgui as per http://trac.handbrake.fr/changeset/3325
- Due to the fact that currently no quicktime based playback devices (yes, including computers and iphone/ipod/ipad) supports soft vobsubs, "Burned In" is on by default.
- Currently soft vobsubs are shown as supported by VLC (Lunettes) and Mplayer on the mac platform.

git-svn-id: svn://localhost/HandBrake/trunk@3326 b64f7644-9d1e-0410-96f1-a4d463321fa5