Enable separate configuration profiles

One thing that was a letdown for me, after finding fman and realizing that it was quite a treat, was finding that it doesn't facilitate having different configuration profiles. I'm a heavy Total Commander user, and I've got like 7-8 different configuration profiles for different purposes (system, gaming, media, music, etc...), and I've got different pane directories, directory menus, etc., for them. This is integral for my file manager use - I just can't see myself stuffing all the stuff into one big bag.

So what I would propose is being able to specify the location of the user settings folder on the command line, like you can do in TC. On Windows, I start mine with command lines like these, stored as system shortcuts:

C:\totalcmd10\TOTALCMD.EXE -i="C:\totalcmd-profiler\wincmd_system.ini"

I know that implementing this would be trivial, and I'm sure it'd be tremendously useful to lots of people, who use file managers in similar ways. It was touched upon in #371 too, posted a few years back. I think this shouldn't require much time, rather something that one could have added from one day to the next.

The issue names no files or tests. Begin by tracing how fman parses command-line options and chooses the user-settings location; done means separate invocations can load distinct settings folders without mixing profiles.