Improve UX for customizing EditEngine forms a little bit

Summary:
Ref T10004. Tweaks some of the UX a little to be more intuitive/inviting?

• Button says "Configure Form" instead of "Actions".
• Root list is less "developer-ey" and more "explain what this is for-ey".

Test Plan:

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T10004

Differential Revision: https://secure.phabricator.com/D14808