Implement automatic remapping from available dimension groups

If you request data from a dimension group that is not directly stored, but it has another available dimension group sharing at least two dimensions, it should remap the request to that dimension group. A simple version of this will simply automatically change the dimensionsND of the request call, but it should also really work for page accessors in which case you need to create new pages by copying from the pages of the available dimension group. This is needed to make things work like commercial VDS.