Fix the flash on doc page route changes

This is subtle and only occurs on Chrome. To reproduce:
1. Go to the Database -> All Docs page for a database.
2. Click from the All Documents page to All Design Docs.

Click back and forth a few times. Notice that sometimes there's a
sort of quick flash that appears over the breadcrumbs section making
it look a little like the breadcrumbs are being re-rendered.

Closes COUCHDB-2467
Nightwatch test to test lookahead component