remove duplicate licences
is_supported_device returns True for Snom 720
move the sipnotification to the aastra controller
handle answer with devices that are not provisionned
make is_supported_device private
change the argument to _is_supported_device

change from device_id to device since we already have device
remove Snom 720 from this branch

Avoid having a broken cti when merging this branch
remove the unittest for Snom support
check if the plugin is a switchboard before answering

This change will not have a great effect at the moment since
Aastras without the switchboard plugin will not answer anyway
but it is necessary with the soon to come Snom switchboard
to avoid answering with the headset everytime someone does
an originate
add a BaseController class for devices controllers
change answer to get_answer_fn in device_manager

Remove the answer function from device_manager
Add the get_answer_fn function to device_manager

This change is required to set the callback function on the connection instance
to avoid querying provd too often
add _get_answer_cb to interface_cti
set the answer callback function in the CTI instance
handle users with no device or no line