test(rxBreadcrumbs): names, count, and main

This is to make rxBreadcrumbs easier to bring into apps that need to
assert breadcrumb status on a page. It uses the same approach that
rxPage uses to pull in the default element, since there's likely only
one on the page, and there's only a couple things that matter.
Merge pull request #545 from Droogans/e2e-rx-breadcrumbs-main

test(rxBreadcrumbs): names, count, and main