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