Add Reporting Mode

* Add a new operating mode to rippled called reporting mode
* Add ETL mechanism for a reporting node to extract data from a p2p node
* Add new gRPC methods to faciliate ETL
* Use Postgres in place of SQLite in reporting mode
* Add Cassandra as a nodestore option
* Update logic of RPC handlers when running in reporting mode
* Add ability to forward RPCs to a p2p node

cfg/initdb.sh

@@ -0,0 +1,10 @@
+#!/bin/sh
+
+# Execute this script with a running Postgres server on the current host.
+# It should work with the most generic installation of Postgres,
+# and is necessary for rippled to store data in Postgres.
+
+# usage: sudo -u postgres ./initdb.sh
+psql -c "CREATE USER rippled"
+psql -c "CREATE DATABASE rippled WITH OWNER = rippled"
+