Fix broken profile images

This PR adds javascript code that detects broken profile images on
the site, and requests the server for an updated profile images.  The
server makes and API call to the HS server to obtain latest user
information for the corresponding user and returns a new image url.

I've tested locally by saving broken URLs for my profile image locally.  
The easiest way to test this would be to deploy it on staging, and see 
the broken profile images get fixed slowly, if everything is working, as 
expected.