Improve "other org" sign-up workflow

[cmsetzer]

This branch makes several changes to the firm sign-up process:

• Removes some use cases (journals, faculty) from the Sign Up section and retitles the Law Firms section as "Other Orgs."
• Updates the Sign Up for Free section on the Perma landing page to reflect the above changes.
• Updates various copy text and links to reflect the above changes.
• Modifies the sign-up form on the Other Orgs (formerly Law Firms) section to include more detailed information, and includes that information in the email it generates.

To validate

Run Perma locally from this branch and inspect the updated sections:

• Sign Up for Free section on Perma landing page
• Other Orgs sign-up form

You can validate the form-generated email by submitting the form and then checking your terminal output for the rendered email body.