Reworks to the shuffle system to improve performance and allow fast shuffling from a big library (but this work for all database views)

This improvement brings a huge performance improvement to start a random mix of your library. Previously, the only way to do this was to increase the size of a playlist with absurd sizes number. Now it will respect the limitation but will insert random songs from the current view.

Database: Add true random songs in playlist if it is gonna exceed its maximum capacity

More context is available here : https://www.reddit.com/r/rockbox/comments/1ez0mq4/i_developped_true_full_library_shuffle_for/

Also :
- Improved layout in the DB browser
- New default max playlists capacity is now 2000 on old PortalPlayer targets to give a better user experience and not having to wait dozens of seconds while creating a playlist
- "Show insert shuffled" option is now true by default
- Add a new shortcut to play all songs shuffled in the DB browser
- Now the feature is fully optional and enabled only on targets that have more than 2MB of RAM
- Add entries about this feature in the manual to explain it to the users
Change-Id: I1aebaf7ebcff2bf907080f1861027d530619097c

Change-Id: I3354923b148eeef1975171990e814a1a505d1df0

apps/settings_list.c

@@ -1120,7 +1120,11 @@ const struct settings_list settings[] = {
     SYSTEM_SETTING(NVRAM(4), topruntime, 0),
     INT_SETTING(F_BANFROMQS, max_files_in_playlist,
                 LANG_MAX_FILES_IN_PLAYLIST,
-#if MEMORYSIZE > 1
+#if CONFIG_CPU == PP5002 || CONFIG_CPU == PP5020 || CONFIG_CPU == PP5022
+                  /** Slow CPU benefits greatly from building smaller playlists 
+                  On the iPod Mini 2nd gen, creating a playlist of 2000 entries takes around 10 seconds */
+                  2000,
+#elif MEMORYSIZE > 1
                   10000,
 #else
                   400,
@@ -1854,7 +1858,7 @@ const struct settings_list settings[] = {
                   true, "warn when erasing dynamic playlist",NULL),
     OFFON_SETTING(0, keep_current_track_on_replace_playlist, LANG_KEEP_CURRENT_TRACK_ON_REPLACE,
                   true, "keep current track when replacing playlist",NULL),
-    OFFON_SETTING(0, show_shuffled_adding_options, LANG_SHOW_SHUFFLED_ADDING_OPTIONS, false,
+    OFFON_SETTING(0, show_shuffled_adding_options, LANG_SHOW_SHUFFLED_ADDING_OPTIONS, true,
                       "show shuffled adding options", NULL),
     CHOICE_SETTING(0, show_queue_options, LANG_SHOW_QUEUE_OPTIONS, 0,
                       "show queue options", "off,on,in submenu",