Add initial Conan integration (#712)

Fixes #645

unittests/rpc/handlers/SubscribeTest.cpp

@@ -615,6 +615,7 @@ TEST_F(RPCSubscribeHandlerTest, StreamsLedger)
         auto const handler = AnyHandler{SubscribeHandler{mockBackendPtr, subManager_}};
         auto const output = handler.process(input, Context{std::ref(yield), session_});
         ASSERT_TRUE(output);
+        // FIXME: fee_ref is missing now. this is possibly correct. need to confirm:
         EXPECT_EQ(output->as_object(), json::parse(expectedOutput));
         std::this_thread::sleep_for(20ms);
         auto const report = subManager_->report();