PathRequests object to own all path requests.
Add directory and order book iterators
This should fix the crossed order book bug.
* Change OfferCreate::takeOffers to use new iterators
* Change NetworkOps::getBookPage to use new iterators
Make offerDelete and fill Items more robust.
Handle offers in order books but not in the ledger proper
If we find an offer in the book but not the ledger, deindex it
Reduce log priorities.