bug 1031972 - Problem with paging the task list when multiple checkboxes are used for the filter

Replace call to `urlparams`, since it discards repeated url query keys

This alternative just adds/replaces a 'page' key in the existing query string, keeping everything else intact. 
@mjzffr This is still relying on `request.path`, whereas the original `urlparams` does not (I believe). I'm not saying that's a problem, but I think we're not sure about whether it is or not, which is why I suggested you ask in #playdoh about it, just to be sure. Can you do that before we go ahead and merge this?