Code review comment for lp://staging/~brian-murray/launchpad/bug-supervisor-nominate-for-release

I've updated the branch per our discussions so that only bug supervisors, drivers or owners see the +nominate link and can nominate a bug for a release. I also created 2 more permission classes NominateBugForProductSeries and NominateBugForDistroSeries. Also due to the changes in not allowing just anyone to nominate a bug for a release I had to modify a couple of tests (bug-nomination-views.txt and bug-nomination.txt).