Add RPC "accept_ledger" function which processes all pending transactions (in standalone mode only)

and closes the ledger, opening a new one. The sequence number of the new open ledger is returned.

src/Application.cpp

@@ -162,7 +162,6 @@ void Application::run()
 	{
 		Log(lsWARNING) << "Running in standalone mode";
 		mNetOps.setStandAlone();
-		mMasterLedger.runStandAlone();
 	}
 	else
 		mNetOps.setStateTimer();