English.
Default to "MP4 Audio" when single audio tracks get muxed.
Split up a huge constructor into small bits.
Comment.
Implement drag & drop somewhere else...
English.

The user needs to drop the files here, not just drag them :)
Cleaner TrackWidget constructing.
Renamed setupActions() to the more clear setupActionsAndMenu().
Style.
Cleaner MP4Muxer.
Print cli in- and output when debugging.
Updated error checking when muxing.

Before, muxing a file called 'Error.mp4' or 'WARNING.mp4' would have
always ended in failure.
No need for that just yet.
In the future, MP4Muxer & MP4Extractor should report progress.
Implemented progress indicator parsing.
Fix a bug where the progress bar wouldn't hide after finishing a job.
Unnecessary.
Implemented better progress reporting.

To be tweaked :)
Show or hide the current jobs only when the user wants it.
Apply settings without a required restart.