Dynamic proxies for agents

[bojidar-bg]

It might be nice to have a dynamic proxy for IAgent-s, so that code which uses a remote agent is cleaner.
For example, this would allow writing:

dynamic agentProxy = ...;
Assert.Equals((int)await agentProxy.Neg(1), -1);
Assert.Equals((int)await agent.Add(1, 2), 3);
await agent.Print("test");

instead of:

IAgent agent = ...;
Assert.Equals(await agent.CallFunctionAsync<int>("Neg", 1), -1);
Assert.Equals(await agent.CallFunctionAsync<int>("Add", (1, 2)), 3);
await agent.CallActionAsync<int>("Print", "test")

(Note that for return types, we should probably use a second dynamic proxy as outlined in this StackOverflow question; see also #75)