[AnalogSensors] renamed AnalogChannelAnalogSensor to BuiltInAnalogSensor
[AnalogSensors] fixed API documentation in AnalogSensors.h
[AnalogSensors] fixed API documentation in MockAnalogSensor.h
[AnalogSensors] Added early stage MCP3428 code

- MCP3428AnalogSensor class allow to handle an analog sensor wired to a
MCP3428 I2C ADC (fully implemented)
- MCP3428 class allow to drive an MCP3428 I2C ADC (only partially
implemented, still not working)