Follow-up to 3d9585acbe.
* Avoid deprecated method StatusValue::getErrors()
* Don't use exceptions for control flow
* Don't re-use Parsoid's ResourceLimitExceededException,
it seems unexpected to me and might limit future refactoring
* Use dieStatus() instead of dieWithException(), which will produce
better localised error messages
* Add missing error handling in ApiDiscussionToolsThank
Change-Id: Ia032025f92f1c3cc0d62a0f45925dddba93fb42f