[Cashtab] Better formdata organization in create token form

Summary:
T3528

We have many state fields different form data input and errors. We do not need so many. Combine string form data items into one object. Combine input handling into one function.

This will make it easier to support additional token genesis tx types, like NFTs.

Test Plan: npm test

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Subscribers: emack

Differential Revision: https://reviews.bitcoinabc.org/D16000