Fixed answer sorting

Since we now load the answers section of the questions editor with ajax,
the jquery to make answers sortable needed to change. Instead of calling
once on ready, it needed to be called every time the div containing answers
was reloaded.

	app/controllers/answers_controller.rb: added a controller with one
	method - sort

	app/views/questions/_answer_fields.html.erb: added a class to the
	icon serving as a handle so it could be identified to the sortable
	ui.

	config/routes.rb - added route for answers#sort

	lib/assets/javascripts/surveyor_gui/surveyor_gui.js: made mods to
	call sortable when reloading answers with ajax.