mpc-walkgen entire refactoring

Change-Id: I4c16210fa5969bf66ff4497ca43ce4ef5d47fbfa
Remove the old mpc-walkgen (need sync with naoqi)

Change-Id: Id234881fe2d8b208513ba2d300a0eea56f1b45c4
Add a 2-mass model

Change-Id: Ie1d588526a755eaef7e509895bd186f5968450bf