diffs: compare overhaul....
diffs: compare overhaul.
- made compare and commit range pages more consistent with other commit diff pages
- removed mergerly, closes
#4665. Old diff2way is replaced by new diffs with
side-by-side mode.
- cleanup button behaviour on compare page. Added help text and
generally improved UX
- switched file-diffs to compare page with file filter. Part of
#4000
- added collapse/expand commits buttons in compare views.
