Clean up collection view

1. Remove `renderAndInsertItem`. This is extremely simple one-line shortcut without side effects that can be replaced by similar simple code. I removed it because there are a lot of methods in collection-view already.
2. Rename `getView` to `initItemView`. There’s `getItemViews` which sounds the same but does the opposite and new name clearly represents what method does: it just initialises new instance of child view.
3. Rename `showHideFallback` to `toggleFallback`, `showHideLoadingIndicator` to `toggleLoadingIndicator`. `toggle` is a good analog of jQuery.fn.toggle() [although jquery.toggle behaves not like our version — it allows to pass boolean params to show-hide and is not event handler like our version, so it would be strange].