Ports from aria-toolkit and enhancements

Added audit for multiple explicit owners.
Added audit for aria-owns DOM descendant.

Enhanced (and renamed) "non-existent-labelledby" audit to cover all id reference types: 
 * aria-activedescendant
 * aria-controls
 * aria-describedby
 * aria-flowto
 * aria-labelledby
 * aria-owns

Added a few utility methods to support some of the new functionality.
Added IE11 support.
Added unit tests for RequiredAriaAttributeMissing audit.
Unit tests for all changes.
That's part of the closure linter tool I believe. I have already made a couple of requests there:
https://code.google.com/p/closure-linter/issues/detail?id=47#c4
https://code.google.com/p/closure-linter/issues/detail?id=82
It felt pretty abandoned there though, tumbleweed.

I'm hoping this will become ingrained but I code for hours every day to a different standard.
Not heard of clang-format - will be checking it out.