plugins & debug menu: apply consistent titles

Purge "Menu" or "Rockbox" from plugin menu titles
and match application names from manual.

Exception: "Main Menu" is left unchanged as the
title for the Main Menu Configuration plugin, since
it appears in Rockbox's Settings menu and therefore
should match the name of the setting.

E.g.:

"Rockbox Goban" => "Goban"
"Image Viewer Menu" => "Image Viewer"
"Viewer Menu" => "Text Viewer"
"Menu" => "Chess Clock"
"Do What?" => "Text Editor"
"Mpegplayer Menu" => "MPEG Player"
"Multiboot Settings" => "Multiboot"
"Disktidy" => "Disk Tidy"
...

Change-Id: Ie6d3be7557f31a36309489037ad8b2b27b06706e

apps/plugins/chessclock.c

@@ -688,7 +688,7 @@ static int run_timer(int nr)
                 /* MENU  */
             case CHC_MENU:
             {
-                MENUITEM_STRINGLIST(menu, "Menu", NULL,
+                MENUITEM_STRINGLIST(menu, "Chess Clock", NULL,
                                     "Delete player", "Restart round",
                                     "Set round time", "Set total time",
                                     "Playback Control");