Export initReportIssueLink function

Summary:
If we want to render an additional link for reporting an issue, this
needs to be re-usable.

Test Plan:
loaded learning dashboard, opened an exercise, made sure it worked
via Chrome web inspector, added a link on the page with an id "komalo"
in JS console, ran Khan.initReportIssueLink("#komalo"), then clicked it,
   made sure the report issue form opened

Reviewers: alpert, eater

Reviewed By: alpert

Differential Revision: http://phabricator.khanacademy.org/D2534