Add Helper method "Fragment" to wrap list of react child components

[Javaherr]

React has this Fragments to group a list of children without adding extra nodes to the DOM.

It would be really helpful to have Fragment helper method in both @cyclejs/react-dom & @cyclejs/react-native to wrap an array of child components in it.

Without it if we wrap an array of child components in div or View we get into "Each child in an array or iterator should have a unique key prop" issue.