Use a stock GTK+ dialog

Use the stock OK/Cancel GTK+ dialog instead of making our own.  Also
use the response from gtk_dialog_run() to decide whether to save instead
of using custom callbacks for the buttons.  Should make the dialog more
Maemo 5 friendly.

Also, eliminate some unnecessary crap in the hildon-control-panel plugin
path, and reintroduce do_reconfig() in preparation for adding HUPing of
a running browser-switchboard.