Input handling

We have realized that the only way to handle input is to do so in the player prefab.
To us this feels awkward. The player prefab is instantiated, one instance per player but the OnSyncedInput is only invoked on the local player (obviously), so basically we have numPlayers - 1 garbage instances.

We would much prefer to be able to assign a class instance or delegate to be the input handler and have TrueSync call that each synced input.