Calculation of the mass of a portion of the kinematic chain

[rafaelxero]

There are three main changes:

• The update of ptr->vo and ptr->w in Body::calcInverseDynamics as I think they were missing,
  as confirmed by comparing with results in Matlab
• The addition of JointPath::calcJacobianDot, which hasn't been tested yet but it is not used
• The addition of LinkTraverse::calcTotalMass, to get the mass of a portion of a kinematic chain
  (I use it in hmc2/Util/multi_contact/multi_contact.cpp)

[fkanehiro]

Please update this PR to pass Travis.