Fix FFmpeg Thumbnal AR

Fix aspect ratio of thumbnails generated by FFmpeg, just like MPlayer
does (fitting the thumb in a 320x180 rectangle with black padding).
Fix FFmpeg subtitle convert

Added a stopProcess() at the end of FFmpeg subtitle SRT to ASS
converting process. Without this, a pipe is created and a timer keeps
messing up the buffer progress bar, showing 0 MB/XX MB intermittently.
We can see this happening both in GUI interface and trace log when
playing a video with on-the-fly conversion of SRT subtitle to ASS with
FFmpeg.
Update pom.xml with new Dependency link
Merge pull request #293 from Optimusprimeums/pom_update

Update pom.xml with new Dependency link
Merge pull request #291 from tdcosta100/fix-ffmpeg-subtitle-convert

Fix FFmpeg subtitle convert
Merge pull request #290 from tdcosta100/ffmpeg-thumbnail-ar-fix

Fix FFmpeg Thumbnail AR