Rework execute_action_group

[tetienne]

See https://github.com/iMicknl/python-tahoma-api/blob/master/tahoma_api/client.py#L104

I suggest renaming this method to send_commands. It will be more user friendly.

• This method must take also a device url as parameter. It's not the case.
• A list of Command is taken as a parameter, must not convert as a json when set in the payload.

{"label":"Volet du bureau - Régler à 28% - TaHoma PC","actions":[{"deviceURL":"io://xxxxxx:5978000","commands":[{"name":"setClosure","parameters":[28]}]}]}