Fixes for running mtt from the docker-compose

[h2g2bob]

Thanks for making a really useful library!

I had to fix some stuff when I tried to run mtt using docker-compose.

The main change is moving the .secret files into a config/ subdirectory.

This would be a breaking change for existing users who have .secret files in the root directory (even if they don't use docker-compose). I've added a mitigation of: if it looks like config is in the old location, use the old config (and print a warnings.warn()).

It (hopefully) wouldn't break anyone's setup, but does add an ugly cludge into the file.