lastfm_scrobbler speed up track culling, better duplicate logic

rather than going through the whole file each time we can just walk
through the remainder speeds up duplicate removal by quite a bit

check timestamp of tracks to not remove multiple plays of the same song
at different times, unless back to back (then its probably a resume after
shutdown)

devices without RTC use current_tick but thats in centiseconds
convert to milliseconds so we can use the timestamp in the above calculations

my fix to the scrobbler_viewer makes the include menus disappear as
soon as you hide columns so explicitly mark if we are
dealing with a scrobbler log at load

Change-Id: I11bbebe9af45945a7e1326a5e419290086b05aaa

apps/playback.c

@@ -1259,7 +1259,7 @@ void add_playbacklog(struct mp3entry *id3)
     if (!global_settings.playback_log)
         return;
     ssize_t used = 0;
-    unsigned long timestamp = current_tick;
+    unsigned long timestamp = current_tick * (1000 / HZ); /* milliseconds */
 #if (CONFIG_STORAGE & STORAGE_ATA)
     char *buf = NULL;
     ssize_t bufsz;