Simplify React components

[MadeByMike]

There are some pretty big and complicated React components here.

Many of these can be simplified. Some ideas:

• Remove render props pattern from RSVP
• Use a form library (maybe Formik?)
• Split up the index page
• Remove nested ternaries and otherwise improve code readability

If we can agree on a list here I'll make an issue for each. These are good first issues.