"working" scenarios:
---------------------
vase on a table

chairs around the table
plates edge of table


implemented predicates:
------------------------
center of
on top or
around
beside
edge of
corner of
below


- added collision detection


TODO:
-----
- handling rotations
- loading object data (i.e. dimensions)


to handle rotations: 

first assume no rotations, then rotate everything by object's rotation
around object's position.

Check for collisions now.



collision checking:
need to apply both predicates before collision checking
can apply directly to subject, the placement methods should not rely on subject's current positioning.