With this change, Element now creates cross-signing keys during auth flows for
password login. For other auth flows like token / SSO, it will not happen until
a cross-signing / secret storage dialog flow as before.
Because the tests are run directly by node, we have to use the CommonJS module syntax. We could run the thing through babel, but then we just have another babel.
Windows instructions are from experience and may not be optimized.
We use `export default` begrudgingly here. Ideally we'd use just `export`, though this entire SDK expects things to be exported as a default. Instead of breaking everything, we'll sacrifice our export pattern for a smaller diff - a later commit can always do the default export -> regular export conversion.
