Add buttons to group warning by project or severity.

* Add more project patterns.
* Add more top level comments for global variables and functions.
* Resequence severity numbers to match the dump order.
* Emit warning messages and tables to static HTML JavaScript arrays.
* Replace old static HTML table dumper functions with
  new dynamic HTML JavaScript to generate sections of warnings.
* Warning messages are grouped into sections by severity or projects.
* Better descriptions for SKIP warning patterns.
* Replace output function with print.

Bug: 31377083
Test: run warn.py --byproject build.log
Change-Id: I7b44ef6223d5b2f1aa31655a5a47d854f9a1dedc