Display failing checks below the roleout

Not sure why there were being hidden. Despite the sum of critical counts
doesn't match the one in the translate action, or the sum of critical
counts in the stats table that is because here we show the number of
critical errors, and in the other two places we instead show the number
of units with critical errors (it is possible for a unit to have several
critical errors).
Only highlight in red the critical failing checks
Cleanup: Remove unused imports
Cleanup: Use decorator to register template filter
Cleanup: simplified condition
Cleanup: removed unnecessary extra variable
Cleanup: removed page zoom feature

Conflicts:
	docs/upstream_differences.rst
	pootle/static/css/editor.css
	pootle/static/css/style.css
	pootle/static/js/README
	pootle/templates/layout.html
Docs: Add missing items to release notes
Last action: be explicit in which context it's adjusted
Buttons: ensure button colors persist for anchors