Instead of implementing hand knitten calender widgets i would prefer to have 'input type=date' in the grid.
I did apply a patch in pqgrid.dev.js (version 8.1.2) line 5089 -->
inp = "<input class='" + cls2 + "' " + attr + " " + style + " type="+(objP.column.dataType=="date"?"date":"text")+" name='" + dataIndx + "' />" //rh use html5 data input widget in modern browsers
but thats just a quick and dirty solution.
Maybe you take this as a feature-request?