Two link checker curation tasks:
- A basic link checker that checks that any value of anyschema.anyelement.uri returns a 20x http status when retrieved. This link checker is also designed to be extended by overidding either or both of the getURLs and checkURL methods.
- A simple link checker that extends the basic link checker, but isntead checks all elements that begin with http:// or https://
(Probably need to think of better names than simplelinkchecker and basiclinkchecker to differentiate between them better.)