Position/collision methods for Things

[LocalInsomniac]

• set_position(x, y, z, [no_interp]) will change the position of the Thing as well as its position in the bump grid. no_interp will skip interpolation if set to true. All Things should use this method from now on instead of directly modifying position variables.
• set_size(radius, [height], [test]) will change the collision size of the Thing and adjust its position if m_collision is enabled. If test is true, the method will fail if the new size doesn't have enough space.
• set_bump_size(radius) changes the bump size of the Thing and updates its position in the bump grid.