Subscriptions: New C# SDK API

[joshua-spacetime]

Implement the new SDK API and WebSocket message handling as defined in the Subscription and Module API proposals.

[cloutiertyler]

We need to implement the mutable subscription API for the C# client. This has become a P0 priority.

The context on why its become high priority is that I need to deliver the Unity tutorial to Freecodecamp for them to make their YouTube video, and either our old API will be immortalized in their video forever or we will have the new 1.0 API ready.

We are planning to support the old API as a backup plan, but we would really rather the tutorial include the new/better/not-deprecated API.