add more ui states
view: add about dialog
README update
soundgst: keep a mmbackend reference

In this way the mmbackend is completely deleted until the class destructor is
called.
widgets: add dialpad widget
view: show & hide dialpad
controller: remove outgoing ring

It collides with the server ring.
controller: remove set_called_parties()
controller: if call failed nullify remote_party

Avoiding the surprising effect of call after the network is setup
Inactive is the initial UI state
widgets: completion popup when down key pressed
gopalmanager: add gopal_manager_send_user_input_tone()
model: add send_input_tone()
controller: handler input_tone callback
README update
makefile: dist target