* parse ledger_index as number
* allow websocket to use "command" or "method"
* mark all non-forwarded responses as validated
* dont mark forwarded errors as successful
* reduce forwarding Websocket expiration 30->3 seconds
* fix merge conflict in test.py
* adds ledger_current and ledger_closed
* deserialize `taker_gets_funded` into amount json
* limit account RPCs by number of objects traversed
* assign result correctly
* Adds a cache for the most recently validated ledger state
* Replaces the keys table with successor table
* Adds support for ledger diffs in the database
* Removes BackendIndexer
