LCL history request and response. (#59)

Detect and request missing lcl history from another random node.
Sending lcl history response to a asked node.
Getting lcl history response and applying it.
Delete lcl that exceeds max ledger sequence.

src/main.cpp

@@ -113,6 +113,9 @@ void std_terminate() noexcept
 
 int main(int argc, char **argv)
 {
+    //seed rand
+    srand(time(0));   
+
     // Register exception handler for std exceptions.
     std::set_terminate(&std_terminate);