Gtk3 migration

GTK 2 -> 3

GNOME Migration guide

• All preparation steps seem to work already (so we hopefully only have to look at the time of migration sections)
• Building with Gtk3 gives no errors during cmake preparations (simply remove libgtk2 and install libgtk3)

Known current issues

• GtkRuler is not supported. Best idea is probably to look at some other opensource project which used GtkRuler and ported it to gtk3 (Inkscape)
  • GIMP commit where GTKruler was ported to gimpRuler
  • ink-ruler.h (Current)
  • ink-ruler.cpp (Current)
  • ruler.cpp (2014)
  • ruler.h (2013)
• Build files with specific errors for Scroom and GtkRuler
• There are two files still using GDK_Drawable_get_visible: gui/source 448 & libs/tiled-bitmaps/tools 26. Change needed to use GDK_window instead