CMake: factor out explanation of skipped modules.

Make a function out of explaining-skipped-modules, and call it
not only after collecting all the modules, but also after
the feature summary, so that it's quite clear which modules
are skipped.

CMakeModules/CalamaresAddModuleSubdirectory.cmake

@@ -1,4 +1,3 @@
-include( CMakeColors )
 include( CalamaresAddTranslations )
 
 set( MODULE_DATA_DESTINATION share/calamares/modules )
@@ -9,6 +8,16 @@ macro( calamares_skip_module )
     set( SKIPPED_MODULES ${SKIPPED_MODULES} ${ARGV} PARENT_SCOPE )
 endmacro()
 
+function( calamares_explain_skipped_modules )
+    if ( ARGN )
+        message( "${ColorReset}-- Skipped modules:" )
+        foreach( SUBDIRECTORY ${ARGN} )
+            message( "${ColorReset}--   Skipped ${BoldRed}${SUBDIRECTORY}${ColorReset}." )
+        endforeach()
+        message( "" )
+    endif()
+endfunction()
+
 function( calamares_add_module_subdirectory )
     set( SUBDIRECTORY ${ARGV0} )