Adds some useful information in polygerrit/rietveld and buildbot UIs. Polygerrit/Rietveld: * Shows which file has been LGTMed by owners, which files are missing owner reviews etc. * Suggests a list of reviewers for files that still don't have an owner as a reviewer. * Allow adding OWNERS to the reviewer list. Buildbot: * Shows the blame-list, and the list of failures for a particular bot. * Links to the changed files from for a particular run in a buildbot.