Add 'Categories:' on waterfall page (like console already).
Items in 'Categories:' are click-able links like '/waterfall?category=...'
so they are convenient to filter your waterfall view.
Screenshot:
http://pix.academ.org/img/2014/07/10/40be2295c6e0de74ef17b8e138f5421c.png
Surround 'Categories:' by 'if categories|length > 1' on waterfall page.
Release notes: add item with description 'categories' link on 'Waterfall' page.
fix more AssertionError's for new-style steps in web status ui

This fixes the following urls:
  http://localhost:8010/builders/<builder name>/builds/<build no>/steps/<step name>/logs/<log name>
  http://localhost:8010/builders/<builder name>/builds/<build no>/steps/<step name>
  http://localhost:8010/waterfall
Merge pull request #1275 from thedylman/fix_new_style_steps_in_web

fix more AssertionError's for new-style steps in web status ui
Merge pull request #1176 from asashnov/eight

Add 'Categories:' click-able links on waterfall page