[test] Add some regression test for issue #426
[core] Compute correctly distance between wheels for WheeledRobot

Fix #426
[core] Improve style of wheeled_robot

- Use PEP008 naming convention
- Add whitespace between arguments
- Remove useless ;
- Wrap long line
[template] Adjust robot template for automatic doc generation

- Add _name entry
- Adapt the indentation of class comment, so the generator will handle
  it properly
[sensor] new collision sensor
[builder] mv set_viewport, properties in bpymorse
[sensor] add collision unit-test

and set collision_property as a component property
(for documentation generation)
[test] reduce time for collision test

and add it to the test list in CMakeLists.txt
[test] revert friction_testing

Shouldn't have been commited at first :D