When starting GUI from CLI, the user may stop it with a keyboard
interrupt. We treat this as equivalent to quitting the application
through the GUI, therefore the interrupt is caught and handled
accordingly.

The implementation required to move some launching code from
"gui.py" to "cli.py", which enabled the reuse of some CLI
methods (_start and _shutdown).

While initializing the UI daemon, syncer errors would be forwarded
to UI clients as part of the client response. This confuses the
clients. Instead of forwarding the error, we now understand it and
change the UI daemon status accordingly.

Move all the console parsing to the CLI code (e.g., argparse)
Modify CLI to be able to launch the session as a daemon, with
    $agkyra start daemon
Modify CLI to provide help for all commands
Implement "agkyra gui" which launches the GUI
Launch GUI when "agkyra" is called without arguments
Update documentation to reflect the changes above

This removes unneeded icons in Mac OSX dock.