libraries/debug.py: Renamed to debugging.py and rewritten

What debug.py was already doing can easily done with the Python's standard
module logging, which actually does it in a nicer way.

This commit adds the decorator `debugging.trace` which will trace the
execution of a function whenever it's called and log it or not, according
to the current logging level.

Currently, we use quite two threads per control, which intermingles the
execution of some of the functions that are meant to use this logging
function. It's because for that reason that it print the name of the thread
where it's executed from.
netcontrol/main.py: Sets the debugging level

By default, the debugging level will be INFO but it can be overwritten by
the user by specifying it with the "--log" flag.

This needs documentation.
core/network.py: Log all activity concerning network communication

This will be useful when the code needs to be optimised. For the time
being, it doesn't seem to be slow, but when more functionality is
implemented, this can come in handy, as well as for debugging purposes.