Added Y-Axis inversion to game.
Renamed World to EntityContainer.

Solves naming conflict with Box2D.
Changed gravity from a scalar to vector.
Introduced Body, width, and height to EntityComponents.
Changed signature of Spawn.
Changed signature of spawn() in EntitySpawner.
Modified EntityFactory to make correct spawn() calls.
Removed unused file.
Corrected LevelLoadingScriptGenerator to use new EntityComponents definition.
Changed Movable and Collidable classes to fit Box2D's model.
Modified EntitySpawners to create Box2D items.
Converted pixel coordinates to meters in LevelEditor.
Added methods to invertYAxis and unit conversion to CanvasInterface.
Corrected CanvasInterface implementations.
Converted ImageItem to use float instead of int.
Implemented Y-Axis conversion in ScrollablePanel.
Implemented Y-Axis conversion in GameCanvas.
Refactored GameViewport to work with Box2D.
Refactored ContentPanel to use meters instead of pixels.
Corrected EntityFactory call to use a muck World.