Modify the softeware architecture

teensy_unit becomes an abstract base class. It handles all the lower
lever controls such as pin assignment, and port function. This includes
turning SMA and LED on and off, and retrieve data from sensors. However,
there's no timing or other behaviours related paramenters.
The Behaviours class will handle all the behaviours related variables,
ones that get exposed to the PC and the timing of actuations.
changed the name from temp_wave to sine_wave
added the i2c library for teensy