DDF-855 Fix schematron validation console logging.

Yes, I did test without changing to Saxon-HE first. Saxon 9.1 is what has the bug. That's really the only directly Saxon thing I changed. It's still using the same ErrorListener, just as an import instead of an inline fully qualified name. The other miscellaneous code cleanup doesn't really affect this bug.

I'm not sure what the best way to unit test this behavior would be, as it involves looking at stdout and whatever slf4j ends up logging to. I guess you could redirect stdout/stderr to inspect them, but I don't think slf4j will let you override where an appender outputs to, that's kind of the point of slf4j.