[AnalogSensors] Refactored classes

- AnalogSensor is no longer an abstract class but has a reference to an
AnalogToDigitalConverter instance and a channel
- AnalogToDigitalConverter is an abstract class allowing to handle any
kind of ADC (with custom resolution)
- BuiltInAnalogSensor is a subclass of AnalogSensor that bypass the
AnalogToDigitalConverter instance to directly use analogRead function
- HMC6352HeadingPseudoAnalogSensor is a subclass of AnalogSensor that
bypass the AnalogToDigitalConverter instance to directly read from
HMC6352 I2C compass
- MockAnalogSensor is a subclass of AnalogSensor that bypass the
AnalogToDigitalConverter instance to directly return a value
- AD7995AnalogToDigitalConverter is a subclass of
AnalogToDigitalConverter for AD7995 ADC
- MCP3428AnalogToDigitalConverter is a subclass of
AnalogToDigitalConverter for MCP3428 ADC