Don't display the 2nd CD by default

[Emilien Klein]

The subtitle upload tab always contains 2 lines, for CD1 and CD2. I'm betting that almost all uploaded subtitles are for a single file, so only one CD. It is very confusing (at least to me) to see that second line when you are only uploading one subtitle. I always ask myself if the program will not register an empty second subtitle, so I alway delete that second line. But since when you click on a line the file selection popup appears, you have to first close that popup and then click on the "minus" button to remove that line.

I believe the default should be to only have one CD, since that accounts for the majority of uploads. If we are worried users that want to upload multiple CD's don't understand they have to press the "plus" button, then maybe SubDownloader should detect that there is a second CD (just like it detects the subtitle file) and add a second line (or more) if it's a multiple CD movie.

SubDownloader 2.0.13 on Ubuntu Linux