Reflow code boxes in Shex page

[tonicebrian]

In order to validate RDF you need the RDF, the Shex and the Shape maps. Right now the UI is designed such that only the RDF and the Shex is at first sight and you need to scroll in order to fix the mappings and to click the validate button.

That creates an unpleasant UX experience because of all the extra gimmicks you need to do in order to use the tool.

Maybe rearranging boxes in a single line and having the validate button at hand could help to alleviate this problem.