Improved registration / new user wizard

[joepio]

Users need to store their secret somewhere safe. The GUI should guide users to do so. We'll need some sort of wizard that clearly shows the secret, allows users to copy / paste (and possibly save to disk?) their secret. Perhaps we should also verify that the user has correctly done so, by pasting the value for verification. This does, however, create some friction in the sign-up process.

Relates to atomicdata-dev/atomic-server#489