gtk3: Fix for deprecated "Gtk::HBox"
Merge remote-tracking branch 'upstream/master'
gtk3: Fix for deprecated "Gtk::SELECTION_BROWSE"
gtk3: Fix for deprecated "Gtk::TextTag::WRAP_NONE"
gtk3: Fix for deprecated "Gtk::TextTag::WRAP_WORD"
gtk3: Fix for deprecated "Gtk::SHADOW_IN"
gtk3: Fix for deprecated "Gtk::POLICY_AUTOMATIC"
gtk3: Fix for deprecated "Gtk::Box#pack_start"
gtk3: Fix for deprecated "Gtk::Widget#modify_font"
Merge pull request #141 from Mazwak/master

Various fixes for gtk3 demo

Patch by Simon Arnaud. Thanks!!!