Add frontend open registration flow

[SuaYoo]

(#28) Initial pass at sign up flow for when open registration is enabled.

@ikreymer I'll leave this open for testing backend changes to send emails. Right now the verify path is configured as /verify?token= but this can easily change.

Flow:

1. User signs up with email and password
2. Sign up success:
   a. If user is not active, shown success message
   b. If user is immediately active upon sign up (checking is_active), user is logged in automatically and redirected to dashboard
   1. user is given option to resend verification email from account settings page
3. User clicks verification email, redirected to /verify
   a. If verification is successful, user is sent to log in page (or is there a way to automatically log them in?)

Manual testing

1. Run app with yarn start-dev
2. Go to /sign-up and sign up. Verify that you're redirected to "my account" on success (TODO UX improvements, maybe show sign up toast, or redirect to a welcome page?)
3. Go to /account/settings. Verify that email shows as "unverified"
4. Click "resend verification email". Verify that status changes to "sent"
5. Go to /verify?token=something. Verify that you see a "This verification email is not valid." error message

Screenshots

Sign up form:

Verification status: