Add `File List name to Windows title bar

[NotNull]

In Everything it is possible to change the Windows title bar with INI entry window_title_format=

One can add the current search ($s) or the instance name ($i), for example.
Suggestion is to show the currently opened .EFU File List (if applicable) with something like $f

[void]

Added to my TODO list: show the current filelist filename in the window caption and add $f for filelist filename to the window caption format.

Thanks for the suggestion.