[XD] Add Extensions Menu

Add Extensions Menu to organize extension commands

Why? When you add extensions, the edit menu grows and becomes very messy

The extensions need to change the following code to use this feature:
```
	var menu = Menus.getMenu(Menus.AppMenuBar.HELP_MENU);
```	
To:
```
	var menu = Menus.getMenu(Menus.AppMenuBar.EXTENSIONS_MENU);
	if(!menu) //fallback to old sprints
		menu = Menus.getMenu(Menus.AppMenuBar.HELP_MENU);
```