Lintrc defaults

Add a config file, containing global default `.lintrc` settings, allowing tool settings to be specified in one location, and only overridden in `.lintrc` files, as necessary.

The example in the test is precisely why we think this would be useful. We have a company-wide `jshint` config.
Heh, yes, I re-factored a bit, and forgot to hook that up again.