Add some objects

[dixx]

Add some more objects of different types into the world.

movable	walkable	interactive	example
no	no	no	flower
no	no	yes	house
no	yes	no	???
no	yes	yes	bridge
yes	no	no	butterfly (maybe better as particle effects?)
yes	no	yes	NPCs, physical traps and moving barriers
yes	yes	no	moving platforms
yes	yes	yes	???

This will help to find abstractions for loading objects.