simplay / simplay-web: define entity size

[moschi]

Currently, all entities are sized depending on the size of the cell their located at. It might be useful, to override this default behaviour and have larger, and smaller entities.

DoD:

• idea is elaborated and discussed
• a proposal exists of how to implement the feature, or it’s decided to not do it
• a proposal on how to handle the Z axis is created
• follow up tasks created