TokenWrapper: display current user balance of outside or wrapped token

[sohkai]

See design.

We should implement the user balance, "max" button, as well as error states if a user attempts to wrap too many tokens (see how the Token Manager manages error states.

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Note that the "max" button implementation will be a bit interesting, due to the current step validation declared on the input. If the user's balance has a lot of decimal places, our current maximum step amount (1e-6) will not work as it will ask the user to round up or down.

The easiest way around this is to detect if the input amount is the same value as their balance amount, and remove the step field if so.