Balanced: Create remote test for voiding a capture

This PR is a work in progress.

I'm not sure if this is even allowed in Balanced.  We're currently
getting an exception when a customer is attempting to void a capture.

I added a remote test which is failing like it is for us in production.

It looks like the void is looking for a void_url which should be the 3rd
part of the authorization.  When the capture is run, its authorization
looks like this: `|/debits/WD3sj4iiNMaatiMGGvNFw2W1/refunds|`
so that last part is empty.

I haven't been successful in locating a Balanced example in the
docs for voiding a capture.  I see examples for voiding an
authorization.

@steveklabnik, might you be able to assist?  I have 2 primary
questions -

1.  What should happen when someone attempts to void a capture?
2.  Might you be able to help with the solution if voiding a capture is
a legitimate operation?  Should the capture be remembering more
so that its authorization has a void_url (not sure that's possible). 
Or does the void need to be enhanced?

Thanks!