Switch to -magnification instead of -deltaZ for mac osx pinch-to-zoom

Using pinch-to-zoom in LibreOffice result in following warning in terminal:
soffice[2376:507] -deltaZ is deprecated for NSEventTypeMagnify.  Please use -magnification.

Following https://groups.google.com/a/chromium.org/forum/#!topic/chromium-reviews/lMxCG03aZNs
-deltaZ is deprecated since OSX 10.6. Therefore use -magnification. The forum also
mentions the fact the steps are 500 times smaller. Lets use this factor 500 to keep the
behavior as consistent as possible

Change-Id: Ie769c518492e5b149a5301b19cae8d841047cb22
Reviewed-on: https://gerrit.libreoffice.org/8345
Reviewed-by: Norbert Thiebaud <nthiebaud@gmail.com>
Tested-by: Norbert Thiebaud <nthiebaud@gmail.com>