Update DataGrid.rst

This is to fix the @import issue for CSS files and it concerns only the first 7 of the 12 examples on the page. Latter 5 work fine (as they don't use explicit styling).

For this fix, I put the @import back in for <link> tags where an explicit CSS styling is required, e.g. #gridDiv{height:20em;}. I have also replaced baseUrl with dataUrl in curly brackets, however I had no way to test it locally. If this fix can not resolve the issue, I need help/ideas!

(I setup rstwiki locally, but it doesn't allow running examples like it is on the website, so can't test it. Is this normal or is my rstwiki setup incorrect?)