and into includeable .hlst files, add them to
postprocess/CustomTarget_images.mk
to continue only including used bitmaps in icon-theme zips

Change-Id: I5c24c3eca93a9c4101bcdcacb0e4b2712133968e
Reviewed-on: https://gerrit.libreoffice.org/36941Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>