Move the SoT Execution in a thread

  - Pr2ControllerPlugin calls Pr2ThreadedSoTController
  - Pr2ThreadedSotController creates a thread that runs
    the SoT to allow a frequency adpatation between
    the realtime Pr2 controller and the SoT
Merge branch 'groovy' of https://github.com/francois-keith/sot_pr2 into groovy
Add support of the grippers

Conflicts:
	src/dynamic_graph/sot/pr2/pr2_tasks.py