Complex selectors & API improvements

• $ selectors now support simple space-separated sequences, like in $( '#a .b #c' ). Still, repeated ad-hoc requests are not recommended, use elements group pattern instead.
• $ function now support optional second "root" parameter. $( '#a', $( '#b' ) ) works the same as $( '#a #b' )
• new view.onRender() lifecycle hook should be used to add DOM-manipulations on view.render()
• view.render() is no op when the watch screen is off for every view. As before, Application.instance.render() will be called automatically when the screen goes on.