Added item key check in internal each loop

[jthawme]

I needed to invalidate the data in a more intense way in the loop, so needed to have the loop give a key from my array of data.

Seperated into a branch now, so it has my specific commit

[tje3d]

This way you cant use the row as key

[jthawme]

Good point, possibly it'd be better to pass in a keyExtractor like callback then. Will try give it a go