plugins: properties: show track info for whole playlist

Track Info can now be displayed for the set of
all tracks contained in a  playlist. This lets
you calculate a playlist's length, for example,
even if it is not currently playing.

This functionality can be accessed from the
existing "Properties" screen for a selected
playlist file. A line has been added at the
very bottom to show Track Info.

Change-Id: I311532b7cfa9e29d46c0cd5623ba4c06c1dd5b5f

apps/plugin.c

@@ -838,6 +838,7 @@ static const struct plugin_api rockbox_api = {
     playlist_get_first_index,
     playlist_get_display_index,
     filetype_get_plugin,
+    playlist_entries_iterate,
 };
 
 static int plugin_buffer_handle;