Fix Herdt's PG final position and running signal

Hello,

These patches change two things:
- "fix" the final position of the CoM, without the patch the robot stops in a crooked position when stopping, this patch ensures that the final position of the CoM is set at the center of the two feet. To do this, we check if the PG still has steps to execute, if not we send the proper acceleration to the CoM.
- Set the running value properly, this is used to compute the 'inprocess' signal that indicates whether or not the PG is still processing data.

Both patches have been well tested on HRP2-10.

Note: I initially wanted to split those two patches (as I am not sure if the first one is the best/proper way to do that) but since the second one relies on the first one it was not possible.