allow any element

[lstkz]

Currently, if you provide custom react components under <CSSGrid>, it will throw an error.
The code is here https://github.com/dantrain/react-stonecutter/blob/master/src/utils/assertIsElement.js

The solution is to wrap it with an extra <div>. Unfortunately, it doesn't work well for me because I also use react-dnd, and I have a weird bug on mobile.

Is possible to remove this validation? I am using a fork with this change and it works without any problems.
The custom component must only apply provided style to the main <div>.

[dantrain]

Yes I think this could do with a rethink. Perhaps an API closer to React Motion's render prop would be better? Anyway I will see about allowing switching the validation off and documenting the use of the provided style prop.