fix(gridster): ensure coords instances are destroyed on widgets

…when removing a widget, or when destroying the gridster instance.
Before this change, if you called destroy without `remove` set to true,
coords instances was leaking jQuery data objects.

Also nullified the gridmap, and faux_grid arrays.

src/jquery.gridster.js

@@ -747,6 +747,7 @@
 
         $el[this.options.hide_method]({
             always: $.proxy(function() {
+                $el.coords().destroy();
                 $el.remove();
 
                 if (!silent) {
@@ -3123,6 +3124,11 @@
      */
     fn.destroy = function(remove) {
         this.$el.removeData('gridster');
+        this.$widgets.each($.proxy(function(i, el){
+            $(el).coords().destroy();
+        }, this));
+        this.gridmap = null;
+        this.faux_grid = null;
 
         // remove bound callback on window resize
         $(window).unbind('.gridster');

test/index.js

@@ -328,8 +328,8 @@ describe('gridster.js', function() {
 
             it('should clean gridmap array', function() {
                 this.gridster.destroy();
-                expect(this.gridster.gridmap).to.be.empty;
-                expect(this.gridster.faux_grid).to.be.empty;
+                expect(this.gridster.gridmap).to.not.have.length;
+                expect(this.gridster.faux_grid).to.not.have.length;
             });
         });