LinGui: SRT support

LinGui: SRT support
- there are now two buttons to add subtitles
  one button adds normal subtitles from the source.
  the second adds SRT subtitles.
- when an SRT subtitle is selected in the list, the available controls change
  SRT controls are: Language, Character Codeset, File, and Time Offset (ms)
- A combo entry box is used for character code.  A subset of the most common
  character codes is available in the popup.  Other codes can be manually
  entered in the entry box.
- The last used SRT file directory is remembered.
- Remove the debug printf eddyg left in decsrtsub.c

git-svn-id: svn://svn.handbrake.fr/HandBrake/trunk@2648 b64f7644-9d1e-0410-96f1-a4d463321fa5