Refactor CameraRos constructors.

Make only one constructor which initializes the buffer using
HardwareSensorCamera::init().
Remove start method from CameraRos to use the parent one
Push more for a future where we'll have a comprehensive (and simple) main.hpp file

Still not complete though.

Summary:
- Add a node that uses the simplemain.hpp;
- Add demo_slam_simple_stop;
- Put all parameters used into INIT at the beginning of the file

Missing:
- Displays
- Export things

Bug:
- Crashes with segfault when leaving the program. Something with the
  robot destructor and data logger.
Add run and main functions to simplemain.hpp

Compiles but there's a segfault going on into SensorManager.
Add the README file