Use list in media library when listallinfo is overkill

When the media library is not sorted by mtime and not in two column
mode, there is no reason to use listallinfo/GetDirectoryRecursive,
instead of list/GetList.

Using list instead of listallinfo is desired because listallinfo may be
slow, fetches a lot more data than necessary in this case and because
the MPD reference says this about listallinfo:
    Do not use this command. Do not manage a client-side copy of MPD's
    database. That is fragile and adds huge overhead. It will break with
    large databases. Instead, query MPD whenever you need something.
browser: make sorting optional

This adds a new option, "noop", to browser_sort_mode. If this mode
is selected, no sorting is done in the browser view, and the elements
are shown in the same order as received from the MPD server.