Last bits and pieces to make multiple strums work.

* a (dragstart, dragend) sequence, i.e. without a dragmove in between, is
  basically the same as a click. So adjust the dragend code to deal with
  this case and remove the on click handler.
* The width function on strums now needs an id as we can no longer rely on
  strums.active being set. And in any case, it was wrong in the filtering
  code as it would always get the width of the active strum in stead of the
  current strum under consideration for filtering.
* The ids array must of course be initialized *after* the currently active
  strum has been removed from strums.