Settings menu: add main menu customization
Lets you launch the main_menu_config plugin
from Settings, so that it remains accessible,
even after all other menu items have been
hidden.
Includes minor changes to the main menu config
plugin, so that it better fits in with the rest
of the settings menus:
* Keep theme enabled
* Autosave
* Add "On" or "Off" suffix to each item, to prevent
confusion when Icon_Config is blank, as is the case
with certain iconsets
* Update current selection after swapping items
* Prefix spoken selection with row number for enhanced
clarity when swapping items
* Change title to LANG_MAIN_MENU
* ACTION_STD_OK to toggle an item's visibility
* ACTION_STD_CONTEXT to access options for reordering
menu items, or for reverting to the default menu
* Ask for confirmation before reverting
Change-Id: I74240b94243224c76e23ef8f3a0559bd8ba28df0