Implement a way for activities to have requirements before they can start

[xetra11]

For now the system works like that:

• An urge arises and becomes top priority for an actor
• The activity that matches that urge is being executed for the specified duration

So for now it works like that an activity is immediately executed. However we want some kind of requirement to be fulfilled before that can happen.

Imagine the following:

• Actor Foo wants to wants to eat something urge(eat) == 100
• The eating activity requires food to be available. Either in reach or in an inventory. How this implemented is not important.
• Unless something satisfies the requirement for eating nothing happens.
• There should be a give_up countdown to avert the case where an activity runs forever if the requirement is never fulfilled.
• Now it is possible to fullfill that requirement by simply "remove" it from the requirements list.

So the Goulash consumer would for example read from the engine API that an actor's activity is requiring "food". The consumer's logic can then, for instance move the actor to a food resource. As soon as the food resource is reached, the API consumer can remove the requirement which finally starts the activity as intended.