WinGui: Misc fixes and improvements
- Added "Open This Directory" right click context menu on the destination box.
- Fixed the av_mp4/mkv file extension bug.
- Add new autoname options {time} {bitrate} {quality}

git-svn-id: svn://svn.handbrake.fr/HandBrake/trunk@5653 b64f7644-9d1e-0410-96f1-a4d463321fa5