Implement SSL support for servers and clients

Summary:
This diff implements OpenSSL support in the network stack.
Currently SSL support is only enabled for Bolt connections,
support for RPC connections will be added in another diff.

Reviewers: buda, teon.banek

Reviewed By: buda

Subscribers: pullbot

Differential Revision: https://phabricator.memgraph.io/D1328

tests/concurrent/network_server.cpp

@@ -21,7 +21,8 @@ TEST(Network, Server) {
   // initialize server
   TestData session_data;
   int N = (std::thread::hardware_concurrency() + 1) / 2;
-  ServerT server(endpoint, session_data, -1, "Test", N);
+  ContextT context;
+  ServerT server(endpoint, session_data, &context, -1, "Test", N);
 
   const auto &ep = server.endpoint();
   // start clients