[FIX] initialize unsubscribed order books

Trying to get back to the original state of the order book as when it was created when retrieving an existing order book that had been unsubscribed.  Please review to make sure I have not done more or less than what is necessary for to accomplish that.
Yes, that was the intention - it was called when remote.createOrderBook was called for a previously existing orderbook.  Currently in the client, I set _shouldSubscribe back to true, so that it does call to rippled to reload the orderbook, but this does not appear to be sufficient to set the state back to what it was the first time createOrderBook was called.  I haven't had time to go look at this again, but it still needs to be addressed.