Create form label presentational component and apply it to the register form

This adds a new presentational component app-form-label that attempts to abstract repeated form label html. It then replaces existing html in the registration component thus making it more DRY. It very likely will be used in the mobile app and other web components (not part of this MR)

I originally made a custom thing for the register form, but now it's in forgot password and backup code regenerate page, and can maybe be used in future things.

I made this generic enough that you should be able to use it as a label for any form field, even if it doesn't have "steps". This is untested outside of storybook though!

Probably not perfect, but I can refine it when I pair it with a TextField component.