Protocol: Added method allowing to hangup all calls.
Ekiga: Modified startup sequence and option parsing.

Much of the startup code has been moved to GtkApplication. Options
parsing has been moved there too. --version and --hangup are two new
possible options that can be invoked locally or through a remote
instance.
EkigaApp: Moved assistant display for newer releases to GtkApplication.
Main: Dropped useless variables.