Automated HAR capture for Studio

Collect page load information in HAR files for Studio via bok choy tests.

STUD-2028
Yea, this one is out of date right now.  I've been holding off on merging these changes to edx-platform master... waiting on this PR to get through: https://github.com/edx/bok-choy/pull/53  

The most up to date hash is 83c556d06a8b318f142ff36c5a5677ea014538f5