Added grabber for data saving, better system test

include/driver_simple.hpp

include/grabber.hpp

include/system.hpp

unit_tests/Makefile

unit_tests/main_system.cpp

unit_tests/main_system_stepper.cpp

unit_tests/plot_dynamics.py

unit_tests/single_drum_drive.pdf

unit_tests/single_drum_dynamics.pdf

unit_tests/single_drum_velocity.pdf