Experimenters define transitions: 5pts

[skleinfeldt]

User story:

As an experimenter I can define the transitions that objects can have by specifying 4 things - the states of the actors and targets before and after the transition. The actor is what you are holding. The target is the object in the square you are occupying.

• The actor (what the participant is holding) before the transition
• The target (what is in the square with the participant) before the transition
• The actor (what the participant is holding) after the transition

• The target (what is in the square with the participant) after the transition

  Examples:

• ([empty hand], berry) -> (berry, [empty square])
• (goose, oven) -> (roasted goose, oven)

[alecpm]

I think the work for this is mostly complete in PR #253. I'm not quite sure how to handle picking up multi-use items and it needs some tests for the server side message handlers.