Add support for React elements and arrays of React elements in non-children props

[le0nik]

Right now only children prop is traversed. It is a common pattern to pass react elements in other props. This PR's aim is to add support for this pattern. Non-array iterables are not supported because we can't know for sure how to update their elements and replacing them with arrays might break user's code and expectations.

So these patterns are supported:

// Element
<div el={<span styleName='foo' />} />

// Array of elements
<div els={[<span styleName='foo' />, <span styleName='bar' />]} />

// Array of arrays of elements(deep traversal)
<div els={[[<span styleName='foo' />], [<span styleName='bar' />]]} />

[gajus]

Thank you