Convert Mondrian to use SLF4J.

I hit MONDRIAN-1171, and I wasn't able to patch the relevant 3rd party JARs, so I thought I'd fix Mondrian to use slf4j natively.

This is a work in progress commit for comment; - I suspect the tests don't work as I can't run them. It shouldn't be much work to make them work. If you can give me some pointers to how to run them, I can adjust the patch.