Greatly enhanced (and cleaned up) grasping code for the PR2

Most of the reasoning steps are now moved into the prolog predicates. This makes it more readable, more versatile to use, and it is easier to add and spot special cases.
Added two new features: Maximum object tilt, and robot object grasp distace chk

The robot now is able to judge whether an object is worth trying to be grasped (parameterizable through prolog), and it can process a maximum tilt for objects when moving them with the grippers.