playlist catalog: sort independently from file browser

Allow independent sorting of playlists in the
playlist catalog, using the context menu.

You may want to usually sort playlists by their date
(modified), but sort audio tracks alphabetically.
This is now possible without having to constantly
adjust a setting.

The fact that 'Sort Files' applied to both the file
browser and playlist catalog seems more like a side
effect of the implementation, rather than behavior
that is wanted. Additionally, the 'By Type' sorting
makes no sense when only a single type is displayed.

Since many of the other File View settings don't
apply to the playlist catalog, hide the menu there.

Change-Id: Ic35038015d0860998ae117f472ce23ce3bc80cfa

manual/appendix/config_file_options.tex

@@ -150,6 +150,7 @@
         delete, insert, insert shuffled & N/A\\}
     }
     sort files      & alpha, oldest, newest, type & N/A\\
+    sort playlists  & alpha, oldest, newest & N/A\\
     sort dirs       & alpha, oldest, newest & N/A\\
     sort interpret number & digits, numbers & N/A\\
     tagcache\_autoupdate

manual/configure_rockbox/playlist_options.tex

@@ -7,6 +7,12 @@ related to playlists.
 
 \begin{description}
 
+\item[Sort Playlists.]
+   This option adjusts the sorting of items listed in the \setting{Playlists}
+   menu (see \reference{ref:playlistoptions}). You can also press
+   \ActionStdContext{} in the \setting{Playlists} menu to access the option
+   from there, directly.
+
 \item[Playlist Viewer Settings.]
    This submenu contains settings related to the Playlist Viewer.
    \begin{description}