Fix glib/librsvg deprecation

librsvg: Only inlcude rsvg.h and remove calls to rsvg_init
glib: Remove call to g_thread_init and use g_value_*_schar
Use new GLib threading API

Based on eog commit by Felix Riemann <friemann@gnome.org>
Url: https://git.gnome.org/browse/eog/commit/?id=b5f61d90d0478378cf7cf21bf5ade9eded0ae9f2
Drop support for glib < 2.36
Use gtk_widget_hide instead of gtk_widget_hide_all

gtk_widget_hide_all is deprecated in gtk+2.24 for gtk_widget_hide.
Drop support for gtk+ < 2.24
Remove all calls to gtk_dialog_set_has_separator