exp/services/recoverysigner: reduce duplicate authentication and account conversion code

[leighmcculloch]

The recoverysigner has duplicate authentication and account conversion code. We should think about ways to reduce the code so that the core of what is happening is more apparent.

Note: I don't think we should reduce the duplication if there is no clean way to do so, or if it makes the code horribly more complex.

[mollykarcher]

Closing all recoverysigner issues