enable site-wide bayesian filtering

Create directory in $STORAGE_ROOT for bayes database.

Added --username arg to sa-learn as the user mail does not have permission to edit files in $STORAGE_ROOT. There is probably a better solution to this...
tweak the site-wide bayesian spam filtering config
move sa-learn-pipe.sh from /usr to /usr/local
Merge branch 'jmar71n-master' - site-wide bayesean spam filtering