Refactor LinksController::__scopeTreeToMenu() as Link::setTreeScope()
Move some code to model
Merge branch '1.6-menus' into 1.6

Conflicts:
	Menus/Controller/LinksController.php

Closes GH-229

Ref: GH-222
     http://croogo.lighthouseapp.com/projects/32818/tickets/368-menu-tree-problem