Make the charting wizard available from the XWiki user interface.

The charting wizard is not available from the XWiki interface. This even though we have a lot of code for the charting wizard, and that this code used to work well in pre 1.0 versions of XWiki. It's a real pity to let our code rot like this. Sure, later we can improve it in a lot of ways, but this is no excuse for depriving the XWiki users of functionality that is already implemented and working fine.