align heatmap plot on pixel, similar to plot3d, fixes hover value on margins
align heatmap plot on pixel, similar to plot3d, fixes hover value on margins

radiasoft/sirepo,mkeilman/sirepo,mkeilman/sirepo,mrakitin/sirepo,radiasoft/sirepo,mrakitin/sirepo,mkeilman/sirepo,mkeilman/sirepo,radiasoft/sirepo,mrakitin/sirepo,radiasoft/sirepo,mrakitin/sirepo,radiasoft/sirepo