Explore using react-router for routing instead of routr

[doug-wade]

I think that react-router has become the standard for routing in the React world, and there are a lot more folks familiar with it than with routr. I'm afraid that react-router makes some fundamental assumptions that go against the streaming nature of react-server, but that may have changed, and I may be wrong.

Migrated from #50

[jaredpalmer]

cc @mjackson

[mjackson]

I don't know if anyone from either the react-router or react-server teams fully understands the others' technology. Might take a while to understand the integration points w/out a little guidance.

[SOSANA]

any updates?

[sresant]

cc @dfabulich