[Design Question]: Strictly require default state

[christian-bromann]

After merging #17 we will have a better differentiation between events and state. Both types are very similar, currently the only difference is that if a state property is updated, missing properties are filled up with default values. With events you only get what has been sent over the wire.

Given this marginal difference which might confuse people, I suggest to be more strict when it comes to state changes, e.g.:

• to broadcast and listen to state changes a default value must be given
• properties that aren't defined by the default value are ignored
• no state update is emitted if user listens to a value which was not broadcasted