get_position_orientation and states[Pose].get_value()

[ChengshuLi]

In iG2, get_position_orientation and states[Pose].get_value() return the CoM frame of the base link. In OG, they return the link frame of the base link. This can have implication because the two links can be arbitrarily far away from each other (e.g. the base link frame can be outside the AABB of the object even).