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
Jehan