Create Unity3D Example Game

[Lachee]

Create a basic multiplayer example game with lobby and integrate the Join / Spectate and Join Request features with accompanying text a materials to help people get started.

[Lachee]

This is currently on hold until Lachee/discord-rpc-csharp#8 is resolved.

[Lachee]

This has been partially completed with Lachee/discord-rpc-csharp#21, marking it as done for the milestone as it is not required to release, just a nice to have.

[AdamMichealThompson]

Hi! Would be really great if you could finish this, I tried all day and couldn't get this working. Cheers!