Add waterfall view

This is an intermediate state of the waterfall view, not the final version. The PR is for deploying waterfall view to the metabuildbot, so I can get comments from the community.

Short video:
https://www.dropbox.com/s/0tx6etckm1vnhrg/waterfall.mov

Improvements:
https://docs.google.com/document/d/1fQCyHFoeygP3It5WvkMUaaLS5dnDT11XjhZxl6_YQp0/edit?usp=sharing