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/tagnavi.config

@@ -176,20 +176,21 @@
 
 # Define the title of the main menu
 %menu_start "main" "Database"
-"Artist"   -> canonicalartist   -> album  -> title = "fmt_title"
 "Album Artist" -> albumartist   -> album  -> title = "fmt_title"
+"Artist"   -> canonicalartist   -> album  -> title = "fmt_title"
 "Album"    -> album    -> title = "fmt_title"
 "Genre"    -> genre    -> canonicalartist -> album -> title = "fmt_title"
-"Composer" -> composer -> album -> title = "fmt_title"
-"Track"   ==> "track"
 "Year"     -> year ? year > "0" -> canonicalartist -> album -> title = "fmt_title"
+"Composer" -> composer -> album -> title = "fmt_title"
+"A to Z" ==> "a2z"
+"Track"   ==> "track"
+"Shuffle Songs" ~> title = "fmt_title"
+"Search" ==> "search"
 "User Rating" -> rating -> title = "fmt_title"
 "Recently Added" -> album ? entryage < "4" & commitid > "0" -> title = "fmt_title"
-"A to Z..." ==> "a2z"
-"History..." ==> "runtime"
-"Same as current..." ==> "same"
-"Search..." ==> "search"
-"Custom view..."  ==> "custom"
+"History" ==> "runtime"
+"Same as current" ==> "same"
+"Custom view"  ==> "custom"
 
 # And finally set main menu as our root menu
 %root_menu "main"