menu editor - remove separator button
Hide move up and move down buttons in cinnamon menu editor.

Remove settings tree from app sys, merge settings menu entries with
the applications menu, remove all cinnamon calls to settings tree.
Reenabled move-up, move-down buttons for moving
categories only.  Since apps are alphabetized (for the moment) in the
menu applet, there's no use in allowing the moving
of apps.  Besides, we need to figure out how to fix positionItem
properly.

fixed
Restore the app-sys functions for settings so nothing gets broken -
just return null or empty where appropriate.
Fix comments
Use get_menu_id to ensure uniqueness when comparing menu items.  Check
that the item is a GMenu.TreeDirectory before trying to use its get_menu_id
function.
Improve getIndex function to handle moving applications
as well as moving sub-menus around.  Moving apps is still disabled,
however, until/unless the menu applet supports it.
Remove cinnamon-settings.menu
Rename menu editor modules so there is no chance of conflict with
other 'alacarte' program.
Fix comments for compile error
Merge pull request #1393 from mtwebster/menu-editor-fixes

Re-submission of #1256 (app-system and menu-editor fixes)