Separate the base and ui parts of the Gcr library more thoroughly.

 * This is due to gobject introspection not being able to have separate
   GIRs provide the same namespace, and the desire to conditionally
   build the GTK+ dependent stuff.
 * Partially based on a patch by Mathias Hasselmann
 * Separate GIRs: Gcr and GcrUi
 * Separate libraries: libgcr-base-3.so and libgcr-ui-3.so. The latter
   links to the former.
 * Symlink libgcr-3.so to libgcr-ui-3.so
 * Expose internal symbols in libgcr-base-3.so so they can be easily
   shared by libgcr-ui-3.so
 * Add --without-gtk argument

https://bugzilla.gnome.org/show_bug.cgi?id=688678