Verify Crawler navigates provided sources

[aep7128]

There's a good chunk of sources in our seeds that aren't being navigated properly. A source could fail for the following reasons:

1.) Domain isn't in the whitelist
2.) Crawler isn't navigating far enough (not enough depth)
3.) exception is thrown when trying to parse the source (HTTP error or some other exception)

We should verify that the seeds URLs are 'crawl-able'