Arf/87799/arp 21a

[nihil2501]

Modifications in order (these are just the commits listed out in order):

1. Empty react-router v3 App.
2. Import 21a, overriding intro sign-in. Basic SIP protocol.
3. Support access token refresh & refactor fetchUser.
4. Repair SIP no-auth handling.
5. Comply with log out instruction when SIP notices no-auth.
6. Work around submitted form staleness w/ logo a tag.
7. SIP login links redirect to sign-in.
8. Fix ConfirmationPage submission timestamp proptype.
9. Revert "Repair SIP no-auth handling."
10. Streamline and correct fetch user exceptions.

Future Extensions

• no-auth on submit has incorrect copy for us "Go Back to VA.gov" in GenericError
  • Could we customize this?
  • href will be fine once we have subdomain

SIP (Semi-)Bugs

• no-auth UX no longer shows up (pursuing platform forms level issue)
• SaveStatus shows over-persisted state of previous IPF after starting over
• IPF and form client state persists after submit
• Oddly, all errors on remove API call while starting over become no-auth, even when they aren't and UX is weird here