Speed up generation of comparison output of descriptions with extracted files

[cornelius]

The generation of the comparison output takes about four minutes, when files are extracted. There is no feedback during this time (other than the loading spinner in case of the HTML view). This is so long that it annoys users and makes them to do something else. The generation should be much faster and give immediate feedback.

This issue came up during a usability test of the comparison views.

[mauromorales]

removed the "tracked by SUSE" tag since the card was archived