Moved parameters of WPrefs's expert check-buttons to a single place
The list of options in the Expert tab of WPrefs.app was filled using
hard-coded list of commands with static indexes and the related
usage were spread accross procedures. This was dangerous because
it could lead to mismatched indexes, the list length being also
variable, so it was hard to update.
This patch proposes to group all the options in a single place (a
static const array), so it is easy to add/remove/reorder the options,
and the code just parses this array based on its auto-calculated
size.