OpenMW-CS: Optimize cell reference listing
There is some room for optimization in the reference listing code used for cell rendering, in particular this piece of code. https://github.com/OpenMW/openmw/blob/f6509fe53eeffd1fc3834616b68989b09300087c/apps/opencs/view/render/cell.cpp#L42 loops over all references in the game world and compares their cell names with the wanted cell.
I found that for just Morrowind.esm, this takes ~0.5 sec per cell, which seems a bit excessive compared to the time needed for actually rendering the objects.
For better performance the cell reference model should group references by the cell they are in, just like in OpenMW.
(RM-2474 from redmine: created on 2015-03-30 by scrawl ., )