BGE physics: When colliding, report first contact point to Python
This patch adds two parameters to the functions in the
collisionCallbacks list. The callback function should thus be like
this:
```
def on_colliding(other, point, normal):
print("Colliding with %s at %s with normal %s" % (other, point, normal))
game_ob.collisionCallbacks.append(on_colliding)
```
The `point` parameter will contain the collision point in world
coordinates on the current object, and the `normal` contains the
surface normal at the collision point.
The callback functions are checked for the number of arguments
`co_argcount`. The new `point` and `normal` arguments are only passed
when `co_argcount > 1` or when `co_argcount` cannot be determined.
Reviewers: brita_, campbellbarton
Subscribers: sergey, sybren, agoose77
Projects: #game_physics
Differential Revision: https://developer.blender.org/D926