- don't include <gdk-pixbuf/gdk-pixbuf.h> in headers in app/
- instead, include it in many .c files instead of <glib-object.h>,
finally acknowledging the fact that app/ depends on gdk-pixbuf almost
globally
- fix up includes as if libgimpbase depended in GIO, which it soon will
In order to make a clear separation between the core modules and the
UI modules, move the necessary enums from display-enums.h and
widgets-enums.h to config-enums.h and the files
gimpdisplayoptions.[ch] from the display to the config module. This
removes the config -> display dependency.
This change has three main benefits
* It lets us remove includes of display files from the config module
* We don't have to link gimp-console and test-config with a subset of
object files from the display module
* It is reflected in devel-docs/gimp-module-dependencies.svg that the
application is made up of core modules and UI modules and that no
core module depends on any UI module
