[FIX] trade: bugs on currency pairs and order books

There was an additional bug in ripple lib that was causing the orderbook to not be resubscribed when you return to the trade tab, resulting in stale order books: https://github.com/ripple/ripple-lib/pull/177 

Update: my proposal was rejected, I've added another commit that puts in place a workaround for the issue until we resolve what needs to be done in ripple-lib