Scattershot commit:
* Quick update to android example/prototype to handle ripple.com/concat uris (as per client QR)
* Updates to PaymentFlow to not allow directXRP payments to oneself
* Add stub STOBject subclasses for txns, and ledger entries
* Add stub STArray/STOBject subclasses TransactionMeta, AffectedNodes, AffectedNode
* Add stub TransactionResult class in core
Restructure ManagedTxn:
* Extends from SignedTransaction, which `has a` Transaction (Payment, OfferCreate, etc)
* Has convenience delegate methods for Publisher, exposing interface consistent with Publisher extension
* Transaction manager now has a `manage(Transaction txn)` method
Refactor:
* Move TransactionResult into core where it belongs, migrate all usages.
* Make STObject.ledgerEntryType/transactionType/transactionResult static methods
* Give relevant subclasses delegate methods for above
Add static STObject.transactionFormat method