Fixing issues with proxy server

So the previous PR did not work because of the proxy in place on genomics-status. Two issues : 
1- api calls are supposed to be https, which was not the case
2- the content of self.request.host is actually tools, not genstat. 

So the solution is to give relative urls, rather than absolute ones.

If anyone knows how to grab the hostname from inside a tornado app, I'm interested.