Alternate implementation of pivotable grid

Extension of the idea from pdmcts pull req https://github.com/aphyr/riemann-dash/pull/16 

Works with currentMax, but the implementation is just a bunch of conditionals. Not very elegant!

Also reverts the slur bug I introduced in https://github.com/aphyr/riemann-dash/commit/655865e4f334d344e9833a75c14651eabdad6cfa