DDFileLister: Made 'view file' from the xfer menu actually work when used as a...

DDFileLister: Made 'view file' from the xfer menu actually work when used as a loadable module (FL_VIEW). Updated extended information view for files.
When used as a loadable module, choosing the 'view file' from the file transfer menu (which
calls bbs.list_files() with the FL_VIEW bit), this is now implemented (previously, DDFileLister
did nothing for FL_VIEW).
Also, when viewing a file's extended information, more information is now displayed, to try
to match Synchronet's stock file lister