Allow OS envir substitution in pathnames for Favourites

[pseudosamri]

It would be quite useful,
a) wrt mutliple accounts, and for
b) cases of users that have pre-existing, custom environment parameters, which map to full pathnames,
if you would do lookup's on envir param substitution, in favourites, and indeed, other configuration parameters;

Thus, in case where wife, kids, and i all have differing accounts on the same computer, that:
a) each person could have their won custom screenshot folder; cache; favourites.... (which can be done now)
however, with the suggested improvement, they would all be parametric, so, from an administrative standpoint,
it would be quite easy to set up the config for one account "generically", then simply copy that configuration to
other users accounts.

Why is this important ?
A) it makes setting up accounts simple;
B) it allows migration of information, transparent to users, say to a larger disk, or to usb keychains per person...;
C) it allows paths to non-XnView, but of local interest, like Family-photos; yearbook; bills; clippings; webclippings...
to be tailored to each user... something like
1) favourtieName path associated with that name
eg MyWebClippings %MyBaseOS_Acct%\%MyWebClippings%
where one set the above params, within the users environment....
that can be done by the administrator, or knowledgeable user (that knows how to change envir strings);

D) doing this makes it easy for novice users, and removes the admin overhead for taxes administrators;