Use a more standard approach to save preferences on MacOSX

CFPreferences* seems to be the proper way to handle preferences on MacOSX.
This approach also eliminates a problem where the hard coded preferences
path couldn't be read.

Signed-off-by: Henrik Brautaset Aronsen <subsurface@henrik.synth.no>
[ fixed small coding style issues ]
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>