Starts to log everything on PyPot.

Add a default null logger to prevent undesired logging.

Add logging in the dynamixel package:
- when opening/closing a DxlIO
- when sending/receiving message
- when timeout occurs
- when corrupted data are received.
Change the packet representation so it’s easier to read when logged.
Correct a bug in the packet representation.

Change the way we use format in the logging to enable the lazy evaluation of arguments.
Change the format of the logging for clarity and parsing purposes.
Add the log message at the motor level.
Log the configuration loading.

Add logging info when loading a config file.
Add logging info in the robot.
Add the logging info for the primitives.
Override update in LoopPrimitive

To keep the log consistent, when you override the update method from a
subclass of LoopPrimitive you should call the update method of the
mother class.
Merge branch 'feature/logging' into develop