Code rewritten to fit OOP concepts

all: headers commented (methods and variables)

IMU:
- data treatment redone: offsets and gains found off-line
- ADXL345.h and itg3200.h added in order to clean the code

Encoder:
- CSB now is CSB_PIN

Wire.h and SPI.h added to "utility": no need to add them to the main
script anymore