Shale/dispute evidence submission modifications

It may be easier to review this commit-by-commit.

@jimdanz 
Yes, specifically here. I'll rebase/edit/push

https://github.com/stripe/stripe-java/commit/c446dc77c3e9c817f87832db00cdc7ec818048f8#diff-be338c286171d2395d658e3e2168d399R497