Add a control to show progress / terminal output of compression

[bittner]

When I use version 1.0.5-1.1 (on Ubuntu) the UI visually freezes sometimes when processing an image. Typically, this seems to be when the application crashes in the background. The UI keeps looking like it would still be processing, e.g.

It would be helpful in this case (and also when processing large files, I guess) to have a way to watch the progress of the compression and/or allow inspection of the terminal output of the tools that ran.

A text area being filled with the terminal output would be just great, which can be expanded or collapsed using a chevron icon.