feat(kff.BindingView): implement counting of rendered (filtered) collection
feat(kff.BindingView): implement counting of rendered (filtered) collection

Number of rendered collection items is propagated into an attribute of some model. Model + attribute are specified in element's attribute 'data-kff-count' using 'model.attr' format. Every time a collection is rerendered, the count attribute is updated.

karfcz/kff