Ensure that diff stats can scroll independently of the diff (#8581)

Ensure that diff stats can scroll independently of the diff (#8581)

This PR ensures that once opened the diff stats detail box can be scrolled independently of the diff on the compare page.

Fixes #5532

Details:

* make diff-detail-box the main container
* move file diff at the same level as diff-stats
* make diff-view options sticy again
* make diff-stats scroll if to mouch
* rm useless css info
* less: mv diff-stats to own class
* use new css class
* cleanup less file
* diff-counter: margin-right: 15px;
* make CI work
* make numbers colorful
* add sign (-/+) to numbers