Wait until all models are spawned before unpausing gazebo

[Shane Loretz]

pull requests #106 Adds a script gazebo_unpauser.py that unpauses simulation after sleeping 3 seconds. If simulation is unpaused before the ur10 arms are spawned then they appear to move on their own to positions far away from the correct initial positions and cannot be controlled. The script should use a different strategy than sleeping to make sure the simulation is only unpaused after the arm models load.