Handle dust that is left over from "Max" trades better

[bghughes]

Presently, users trading on Rubicon can have leftover "dust" from transactions in their wallets. This represents a small amount of wei (usually a 1 at the last decimal place) - it is most apparent on "Max" trades in which a user wants to trade all of their tokens in a swap, for example.

This is annoying from a UX perspective and an on-chain solution should be implemented to handle dust better. I see two paths that could offer solutions:

1. Add max function wrappers that take a user's entire balance of whatever token they are trading and handles dust logic
2. Pool user dust somewhere that is not the user wallet after the transaction