`form` component

[rmorshea]

Add a Form component a la react router's.

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Note from @Archmonger:

We have a reactpy-django PR has proven an effective method to generate forms within ReactPy.
In summary, we will need to intercept the <form> onSubmit event, serialize FormData into JSON, transport that form data to back to the server, then re-hydrate the input elements on the server using this new data.
Serializing file fields is a separate problem, and will require additional thought around DDOS prevention.