Updated pieces.txt
Each visual is now larger and can thus hold more artifacts.

Updated PieceFactory's empty piece visual as well to reflect changes to visual

There is a nasty hard-coded flaw in the way Space handles updateStringRepresentation.
This should be fixed..
Added a small comment to WorldTree's confusing initString method
*NOT TESTED*
Implemented all combinations of constraints and aggregate definitions.
Rewrote large portions of WorldTreeFactory.Tile's addToVisual and removeFromVisual methods