Patch to be able to set min/max rows/columns of a gridster widget

This patch allows you to set the min/max rows/columns of a gridster item.  This change sets the minWidth, maxWidth, minHeight and maxHeight on the $elem.resizable() object.  It also adds a change for updating those dimensions when the overall grid was resized, using a broadcast.

One thing to note, I changed the existing minRows/maxRows to minGridRows/maxGridRows as it seemed more appropriate.

- Matt