Basic pass through JSHint

Just put the src/ directory through a basic first pass in JSHint.
Have mostly focused on unused variables, variable re-declarations and invalid line breaks which could have been causing unknown errors.

I don't know if `Wallet.mkSend` even works, simply because the code before this was using the `Bitcoin.` namespace, which doesn't even exist now?

Whole area is in desperate need of tests.

**edit**: Understandable [if this is accepted] that you may want these commits squashed.