Use gdk_window_get_{width,height} also in Gtk+2

It was added in Gtk+ 2.24
Gtk3: Rename callback function to reflect changed signal.
interface: Move/Add comment for each Gtk version
Remove has-seperator property
Gtk3: Fix deprecated hscale use
Fixed graph jump bug caused by label changing height
Removed unnecessary dependency on dbus-glib-1
Update autotools