allow to codesign on Mac OS X Mavericks

codesign on Mavericks wants much more stuff to be signed apart from the
actual Mach libraries and executables. However the signature for those
data-style files are stored as extended files attributes, so one needs
to take special care on how to package the dmg to not break the seal.

Also explicitly remove some files from the signing, to allow adjusting
user-config path or similar or for gallery.

Change-Id: Ic4c4f7718df1bca7ffa2fecd3fb1d616146d7b14
Reviewed-on: https://gerrit.libreoffice.org/7490
Reviewed-by: Norbert Thiebaud <nthiebaud@gmail.com>
Tested-by: Norbert Thiebaud <nthiebaud@gmail.com>