Feature/commands

[AlexandreGerault]

I started to implement a command system to handle the data_received_event.

I created a command_registry which is an object holding commands and used to invoke commands.
The command class does nothing else than calling the command_executor and having a name and a description.
The command_executor class performs the actions.

At the moment this system can't act on any context. I need to make some generic classes for the arguments.