CD-18 Expose aws box url

@vasili-zolotov @d3ming 

This creates a link to the aws box that's created during ci. Right now it uses the users github icon as the button, but this can be changed later with a real icon. (I didn't want to take a stab at art)
Hmm isn't there a better way to grab the domain name?  Would we be able to read from the env variable for PL_ROOT_DOMAIN?