classNames for Cells & Lists should have precomputed classNames option for speed #28
Description
Right now, when merging BEM classNames for Cells & Lists into one string before passing them into the component rendering function, it can add anywhere from 100us to 1ms to rendering times and this can quickly add up on large lists, especially if cache hits miss. Either look up good ways to optimize V8 to deal with this, precomputed it for components that are composed of them, or even do some kind of babel precompiler, and finally if all else fails, add an option for these components that allows passing the whole className in instead.