Merge revision columns in flakiness dashboard

Merge revision columns in flakiness dashboard
https://bugs.webkit.org/show_bug.cgi?id=123360

Reviewed by Simon Fraser.

Merge revision numbers into one cell separated by /, and clearly label them as "latest revisions".
Also add colors for missing & audio failures so that they won't be an empty cell.

* public/index.html:
(TestResultsView._createTestResultHeader): Create a single th for the list of repository names.
(TestResultsView._createTestResultRow): Use single td for all revision numbers.
* public/js/build.js:
(.this.formattedRevision): Don't prefix revision numbers with '@' when we're not in the tooltip.
* public/main.css:
(.resultsTable .AUDIO a): Added.
(.resultsTable .MISSING a): Added.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@158055 268f45cc-cd09-0410-ab3c-d52691b4dbfc