Allow students to use Google SSO for sign up and login.

Corresponding frontend changes for upchieve/subway!1268 (merged)

On the account creation page, students can now select to sign up with Google instead of entering first name, last name, and password, and that form also no longer has "How did you hear about us" and the checkbox for agreeing to user agreements (there is a disclaimer under the submit buttons instead).

If something goes wrong with SSO and/or account creation on the server, the server redirects back to the account page with a URL containing the eligibility data. Then, on the client when loading the student form, if it sees those eligibility query params exist, it will fill in the corresponding data and show an error message to the student telling them to use password flow instead.

If all goes well with account creation, the redirect goes straight to dashboard page (bypassing verify email since it's already verified by Google).

On login page, there is also now the option to sign in with Google. If there is an error, the student is redirected back to the login page with the error status code in the URL.

In addition:

• Updated more styles related to the forms to match the eligibility/account forms done previously, and moved those styles into shared location.
• Some cleanup on StudentForm component, to remove