Allow form configurations to retitle and reorder forms and add preambles

Summary:
Ref T9132. This just makes edited forms do something, albeit not anything very useful yet.

You can now edit a form and:

• Retitle it;
• add a preamble (instructions on top of the form); and
• reorder the form's fields.

Test Plan:
{F974632}

{F974633}

{F974634}

{F974635}

{F974636}

Reviewers: chad

Reviewed By: chad

Subscribers: hach-que

Maniphest Tasks: T9132

Differential Revision: https://secure.phabricator.com/D14503