Close row types for effects of React lifecycle methods
Add UIRef

This commit adds an opaque `UIRef props state` type constructor which represents
a reference to UI component. The following functions available for working with
UI refs:

  * getSelf returns a refernce to a current React component

  * runUI is a handler which gets an UI reference and executes React effects
    with it (it also checks if current UI reference is still mounted and so
    valid)

The motivation for this change is to add an ability to defer React for a some
period of time (XHR, timer).
example/app: update example with references