Show less noise in the flakiness dashboard stats page.

-Don't show WontFix counts in the charts.
-Don't show expectations types whose counts are all 0.
-Rename the navigation links to better match what the page does.

NOTRY=true

Review URL: https://chromiumcodereview.appspot.com/21122004

git-svn-id: svn://svn.chromium.org/blink/trunk@155113 bbb929c8-8fbe-4397-9dbb-9b2b20218538