support rendering after init with promise

[zbryikt]

we may need some object to be used in render after inited.

[zbryikt]

use view.init!then -> view.render!

[zbryikt]

view.init!then -> view.render! may not work since we need by selector initialization especially when selector may changes over time - after all we may not want to call init each time when we want to render, but still want to ensure that initialization is done before rendering for each selector.