widget properties when dropping it into other grid

fix for #924

* updated two.html to have some min/max/id contrain to copy over

TODO: all data-gs- props are there, but the resize/move feedback isn't in sync. I suspec
onEndMoving() not having o.data('_gridstack_node') as the culprit.

Author: Alain Dumesny

demo/two.html

@@ -121,15 +121,16 @@ <h1>Two grids demo</h1>
         {x: 0, y: 0, width: 2, height: 2},
         {x: 3, y: 1, width: 1, height: 2},
         {x: 4, y: 1, width: 1, height: 1},
-        {x: 2, y: 3, width: 3, height: 1},
+        {x: 2, y: 3, width: 3, height: 1, minWidth: 2, id: 'special', text: 'has minWidth=2'},
         {x: 2, y: 5, width: 1, height: 1}
       ];
 
       $('.grid-stack').each(function () {
         var grid = $(this).data('gridstack');
 
         items.forEach(function (node) {
-          grid.addWidget($('<div><div class="grid-stack-item-content"></div></div>'), node);
+          grid.addWidget($('<div><div class="grid-stack-item-content">' 
+            + (node.text? node.text : '') + '</div></div>'), node);
         });
       });