Cleanup modulesets

This MR contains mostly formatting changes and cleanups by

• removing unused repositories
• running/applying the tidy configuration
• ensuring unified quoting style (double quotes)
• usage of empty tags where appropriate ... and overall making sure there is a unified look and feel as far as human error allows.

Luckily, while doing the cleanup I come across a few errors that have slipped in (e.g. broken XML) and can fix them along the way.

The most changes happen in modulesets-unstable as that has apparently not gotten the "reformatting treatment" yet which I introduced quite some time ago to the other modulesets. So it's finally time to make it look like the other two.

As mentioned in the past, tidy is not a perfect tool, but having it do the heavy lifting still outweighs its imperfections (e.g. introduction of empty lines here and there), and it is deterministic. (A fellow dev once told me "Don't let 'perfect' be the enemy of 'good'".)