Align form creation with the prototype

[DavidBiddle]

What problem does the pull request solve?

Closes #41

This cleans up the HTML for the Create and Edit pages, and adds tests. This doesn't strictly match the design in the prototype - since we've currently got two form fields on this page, we have to mark it up slightly differently to comply with the design system, and I've prioritised compliance over visual fidelity here. Once we remove the email field from this page, we can change the design to match the prototype more closely.
The tests don't cover the email field, since we know we're going to get rid of this in the near future.

Checklist

• I've used the pull request template
• I've linked this PR to the relevant issue (if mission work)
• I've written unit tests for these changes (if code change)
• [n/a] I've updated the documentation in (If any documentation requires updating)