New port: Gaupol subtitle editor

Hi, this is a port of gaupol, an editor for text-based subtitle files.
It supports multiple subtitle file formats and provides means of
creating, editing and translating subtitles and timing subtitles to
match video.

This is my first port, so there might be things I missed. I have tried
to follow the porting guide closely. Please have a look and comment.

Thanks,
Anindya