Add option for returning a fragment instead of a div

[hb20007]

A lot of us use create more components that return fragments rather than divs. It would be nice to have a Boolean option to enable this, similar to the existing option of importReactOnTop which is also used to customize the snippets.

[ocamachor]

x2

[neuromagus]

I added this config option in this pull request, guys... #318