Loading and saving ledger and lcl consensus. (#51)

* Ledger saving, loading, consensus with ledger sequence number.
* std terminate exception handler.

src/p2p/p2p.cpp

@@ -116,7 +116,7 @@ void peer_connection_watchdog()
             }
         }
 
-        std::this_thread::sleep_for(std::chrono::milliseconds(conf::cfg.roundtime * 4));
+        std::this_thread::sleep_for(std::chrono::milliseconds(200));
     }
 }