PID tuning on MCU using topics

[fjp]

See #13 and #35

One more thing about configurability. I am planning to use dynamic reconfigure for the PID parameters and everytime a change happens a message could be published to the low-level base controller to update its PID values. This way we could keep the performance up, because the PID runs on the microcontroller and also have configurability in the high-level code. This could be a workaround of rosserial not supporting dynamic reconfigure. But I need to check if this can actually work.