Make breadcrumbs fail nicely without department

Instead of crashing.
Add stub dashboard for Tier 2 Visit Visa
Make module ready event always be async

Need to make sure `Controller.renderModules` cannot callback before it has returned, so make all modules always be ready asynchronously, in particular when they don't have a collection so don't need to wait to fetch.
Merge pull request #489 from alphagov/tier-2-visit-visa

Tier 2 Visit Visa stub dashboard