Topcoder-X signup link in comments

[jmgasper]

When a user that's not registered with Topcoder-X assigns a ticket, we display a message like this:

<username>, please sign-up with Topcoder X tool

What I'd like to have is the link to register with Topcoder-X as part of the comment, generated the same way we do in the Git access control section of the Topcoder-X UI

The updated comment should look like this:

<username>, please sign up with Topcoder-X here:  <Git access link for this project>

[cwdcwd]

this one we might have to think about how we handle in the event that there's terms the user has to agree to before getting repo access... technically they shouldn't be in there and working if they haven't a terms agreement in place but perhaps we can fix that with #46