plugins: Improve usability of iPod keymaps

- Reduce need to press multiple buttons at
the same time to quit a plugin

- Have "Menu" be default way to quit plugins or
to access plugin menu

- Fall back to (Long) "Select" or Long "Menu"
in cases where Menu button isn't available
(e.g. in ImageViewer and many games)

out of scope:
boomshine, lua_scripts, Rockpaint,
Doom, Duke3D, Pacbox, Quake,
Sgt-Puzzles, Wolf3D, XWorld,
Minesweeper, Pixel Painter, Spacerocks

Change-Id: I6d4dc7174695fe4b8ee9cbaccb21bdbfe6af5c48

manual/plugins/logo.tex

@@ -9,14 +9,16 @@ Demo showing the Rockbox logo bouncing around the screen.
     Increase / decrease speed on the x-axis
         \\
 
-        \PluginUp{} / \PluginDown
+        \nopt{IPOD_4G_PAD,IPOD_3G_PAD}{\PluginUp{} / \PluginDown}
+        \opt{IPOD_4G_PAD,IPOD_3G_PAD}{\ButtonScrollFwd{} / \ButtonScrollBack}
         &
     \opt{HAVEREMOTEKEYMAP}{
         &}
     Increase / decrease speed on the y-axis
         \\
 
-    \PluginCancel{} or \PluginExit
+    \nopt{IPOD_4G_PAD,IPOD_3G_PAD}{\PluginCancel{} or \PluginExit}
+    \opt{IPOD_4G_PAD,IPOD_3G_PAD}{\ButtonMenu}
         &
     \opt{HAVEREMOTEKEYMAP}{
         &}