This checks all urls sequentially, which would block the saving for the sum load time of all urls.  I guess we could make these requests in parallel with something like eventmachine, though I'm not sure how much it would complicate things.

A partial fix for this may be to cache the success of resolving the urls (if this happened in the ValidatorsController too - all the urls in this list should have already been checked.

Wrapping these (and ValidatorsController#resolve) in a [cache.fetch](http://api.rubyonrails.org/classes/ActiveSupport/Cache/Store.html#method-i-fetch) would do it.