refactor(kff): include IE8/9 polyfills into kff build

Because CSS class polyfill is needed for IE9 and there was only W3C event polyfill for IE8 left, I have decided to include both of these into kff core.
refactor(kff.View): performance - do not initialize empty arrays in constructor, create them later "on demand"
refactor(kff.View): performance - do not initialize empty subviews array in constructor, create it later "on demand"
refactor(kff.Binder): performance - do not initialize empty events array in constructor, create it later "on demand"
chore(kff.polyfills): add forgotten kff.polyfills.js file