...which uses the logic already available in VCL's ImplImageTree to locate the
image zip files and find fallbacks for incomplete themes and for localized
images.

(cherry picked from commit 6948c546, plus
f5174c89 "...but do not erase localize
attributes from image elements," which is needed to make localized image
references work again)
Conflicts:
	vcl/osx/vclnsapp.mm

Change-Id: Ic1c15fcacb6596a27a2b051093232902202bf472
Reviewed-on: https://gerrit.libreoffice.org/19644Reviewed-by: Michael Stahl <mstahl@redhat.com>
Tested-by: Michael Stahl <mstahl@redhat.com>