Vertex-centered AMR volumes

[jakob0]

The AMR volumes are only working for cell-centered data. Support for vertex-centered data would be a nice feature and the implementation should actually be less complicated than for cell-centered grids.

[johguenther]

Thanks for the suggestion. Indeed, vertex-centered AMR data should be easier.

[carsonbrownlee]

I asked jakob to submit a github issue for his question on google groups. We'll keep this post updated with any progress, and hopefully any other users that are interested can chime in.