WinGui: Fix adding a new VobSub or PGS subtitle, default it to "Burned In" for MP4 files only. Also defaulted Foreign Audio Scan to Burned In for MP4's now.

git-svn-id: svn://svn.handbrake.fr/HandBrake/trunk@5847 b64f7644-9d1e-0410-96f1-a4d463321fa5