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)
The thought here is that if this is not to be PL-specific, then the job needs to tell strider somehow whether to display a link and to what URL. 

We can think more along those lines. Some options for consideration are:
- print url to stdout, could define a specific pattern that strider understands and checks for to avoid false positives, output is already saved to mongo, so have strider front end parse console output whenever rendering a job
- set a specific environment variable that strider expects, have strider check the environment after each step of the job, append state to job object saved to mongo, render using this saved state
- write to a specific file with some markup that strider understands, and have strider check for file after the job is done, save state to mongo, render based on saved state