Integrate variables by volume filter
This issue was created automatically from an original Mantis Issue. Further discussion may take place here.
We need to create a filter that integrates variables by volume of cells, not just adding up the cells. For instance, with AMR data, the integrateVariables filter is useless.
Also, we need to document the integrateVariables filter to clarify whether it does so by volume (which I believe it doesn't, or just by adding up each cell (which I believe it does).