Improvements to nao_controller:
 * Actions can now be preempted!
 * Fixed race conditions when preemption is requested before task starts
 * Set aborted and preempted terminal states if required
nao_controller now uses a lock-free polling implementation when running actionlib tasks
Merge branch 'improved_nao_controller'
Removed leftover import from nao_controller
Updated test_joint_angles.py to test for preemption
Merge pull request #2 from miguelsdc/master

nao_controller: Preemption of actions