Changes made to add basic simulation
Added the world directory to hold Stage worlds for simulations
Bugs fixed: 1) The circle in the Qt application should be correctly
positioned now. It was incorrect before because we were using the left
wheel as a reference point. Now that we are using the center of the
wheels, it is much easier. 2) The correction of orientation by
adjusting the angular velocity was happening even when the robot was
turning. We only want that behavior when the robot is driving straight.
Changes made to have both robots in the simulation. The test1 world has
been added, but need to add a world file for test2. The grid does not
always show up and I haven't gotten the visualizer class set up yet.
Added world file to test2.