Bump underscore dep to 1.6
Tie requirejs to last version that lets the tests pass.

I'm pretty sure this is just greenwashing the tests, but I don't have the time
right now to figure out why they start failing on 2.1.10. Looking at the
changelog, I couldn't find anything that would have caused the failures. They
have something to do with how we fake the loading of components by defining
their modules directly, but I don't see why that stopped working.