Create login and registration flows

[kylemh]

Feature

What should your feature do?

• Create routes at /login, /sign_up, and /join.
• Create a modal-focused login flow
• Redesign and simplify current registration flow
• Add section for data use info
• Collaborate with @Wimsy113 and @LauraUX to ensure design/product vision is being executed properly.
• Be aware of the discussion here and here and here and here and here

[apex-omontgomery]

Also, please include me (for backend things) as we wish to hook certain actions up on a completed registration. Right now we don't have a singular event we can tie to this completed registration and this leads to not knowing exactly when a user is done.

Most likely this will include some minor BE work on changing the api, but I'll make sure that gets done.