[Moco] Support tracking ground reaction moments and/or COPs

[nickbianco]

Currently, MocoContactTrackingGoal only supports tracking the ground reaction force vector and not ground reaction moments or centers of pressure. We can borrow some code from MocoUtilities::createExternalLoadsTableForGait() for this.

[nickbianco]

While we're at it, we should improve createExternalLoadsTableForGait to return the correct GRF torques: currently it is returning the sum of sphere torques which isn't very useful.