RSA Keys -> Numbers Interface

Replaces #1038.

This attempts to address naming while not handling the larger interface question. I'd like to land this to unblock while we continue to discuss the other options. It should be easy to convert if we choose to change this and we can consider it a 0.5 blocker. (a working sub-interfaces example: https://gist.github.com/reaperhulk/1f90d2d03ac9372c30c6).
I actually swapped the approach to sub-interface just now so we could look at it and that caused another rename :)