Find and fix broken docs links to User Guide

Within the UI help tips, I have found several links to documentation which are incorrect and give 404 errors. For example within templates/CRM/Event/Form/ManageEvent/Registration.hlp there's a link to the-user-interface/profiles which should actually point to organising-your-data/profiles. It didn't take me too long to find a handful of other broken links as well.

Rather than combing through all of them by hand, I think we need to do some fancy grep work to pull out all the docs links and programmatically test each of them to report which links are broken.

Maybe this sort of programmatic test could even be incorporated into CiviCRM Core as an automated test. But at least we should do this once because there seem to be quite a few broken ones.