Add Client Server Handshake

[rmorshea]

Current Situation

Currently, as soon as the websocket connects, the client and server start communicating layout updates/events. This does not allow any extra information to be sent. For example, the client and server could confirm that they are compatible by inspecting their versions.

Proposed Actions

Now that we have message types, we can define and handle an initial set of handshake messages between the server and client. These two handshake messages could communicate version information as well as configuration options (e.g. whether to display server logs in the client and visa versa).

[Archmonger]

Closing this since we bundle our own client within our Python package, I currently don't see a reason to implement this.

The only scenario where things could get out of sync is if someone leaves their browser window open through a ReactPy server upgrade. But in that scenario, there's really nothing we can do on the client-side to fix it, so we may as well just let errors happen.

Additionally, adding a handshake would add latency equivalent to an additional two network responses, which would impact our time-to-load.

Will re-open if there is a proven scenario where this adds some benefit.