Have Repeat Shuffle turn on Shuffle

When "Repeat Shuffle" is enabled, it may make sense
to visibly turn on the Shuffle setting once a playlist
ends and starts from the beginning again.

This seems to fix a few issues:

- After (an unmodified) playlist has been shuffled,
bookmarks now behave correctly in terms of restoring
the playlist's shuffled state and using the correct resume
index. This wasn't the case before. The alternative may be
to set the playlist as modified once it is shuffled, to
prevent creation of bookmarks from that point on.

- Lets you return to the un-shuffled state of the playlist at
any point

- Icon makes it easy to tell if the "unmodified" playlist has
been shuffled already, or not, which wasn't obvious before.

Change-Id: I41af04b041fdc7774c9d9267aaf983ec9d402e13

apps/playlist.c

@@ -2874,6 +2874,7 @@ int playlist_next(int steps)
             playlist->first_index = 0;
             sort_playlist_unlocked(playlist, false, false);
             randomise_playlist_unlocked(playlist, current_tick, false, true);
+            global_settings.playlist_shuffle = true;
 
             playlist->started = true;
             playlist->index = 0;