First working POC
agentcallback channels dont return an extension
The source channel is now used to hangup a call
fix test_receiver.py
fix test_storage.py
call.storage new_call cleans up first

If a call is already tracked, new_call will first remove that call with a notification
and a a newly created call
test that handle hangup calls end_call
simplify tests for handle_dial_begin
remove unused imports
add _Channel.__repr__
test call.receiver.handle_{bridge,channel}