Removing the miniLock.user namespace

This is a tiny proposal to remove the `miniLock.user` namespace. The only call to `miniLock.user.unlock(...)` in the codebase becomes `miniLock.crypto.getKeyPair(...)`.

I think `ui.js` can probably accommodate anything that might have ended up in `miniLock.user`. But I might be wrong about that. Do let me know.

These changes kind of help with #30.