added chosen

see https://github.com/harvesthq/chosen
little changes to styles
manually generating select to avoid ember's metamorph tags

using `chosen` here with ember’s metamorph tags results in unexpected
behaviour. Select now is generated manually
using `chosen` on .comprobante_select
As it no longer uses ember bindings, setting `comprobanteId` manually
translated
added jQuery autocomplete

see https://github.com/devbridge/jQuery-Autocomplete
added ItemsController and responding to jQuery autocomplete with ItemAutocompleteSerializer
added Bandango.ItemOnFormMixin and items/form partial
using items/form