This is reapply of 89965f65 with the new moduleset layout.

Added suggests gobject-introspection to gtk+ and gtk+-3 (as configure.in
has GOBJECT_INTROSPECTION_CHECK([0.9.3]).  Therefore every module that
depends on gtk+ or gtk+-3 gets gobject-introspection.

Every module that doesn't depend on gtk+ or gtk+-3 and has
GOBJECT_INTROSPECTION_CHECK I added suggests gobject-introspection.

The modules that have GOBJECT_INTROSPECTION_REQUIRED, I made sure
gobject-introspection is a dependency.