fix(uiGridRow): Fix memory leak

Bindings were being attached to the uiGridRow scope but never removed
because the scope was not being destroyed even though child elements were
being added. This was fixed by creating new scopes for uiGridRow when
compiled/re-compiled.

Also, added an element-based `$destroy` handler for ui-grid-cell. It
already had one for the $scope.

src/js/core/directives/ui-grid-cell.js

@@ -87,8 +87,8 @@ angular.module('ui.grid').directive('uiGridCell', ['$compile', '$parse', 'gridUt
             rowWatchDereg(); 
           };
 
-
           $scope.$on( '$destroy', deregisterFunction );
+          $elm.on( '$destroy', deregisterFunction );
         }
       };
     }

src/js/core/directives/ui-grid-row.js

@@ -24,11 +24,26 @@
             $scope.colContainer = containerCtrl.colContainer;
 
             // Function for attaching the template to this scope
+            var clonedElement, cloneScope;
             function compileTemplate() {
               var compiledElementFn = $scope.row.compiledElementFn;
 
-              compiledElementFn($scope, function (clonedElement, scope) {
-                $elm.empty().append(clonedElement);
+              // Create a new scope for the contents of this row, so we can destroy it later if need be
+              var newScope = $scope.$new();
+
+              compiledElementFn(newScope, function (newElm, scope) {
+                // If we already have a cloned element, we need to remove it and destroy its scope
+                if (clonedElement) {
+                  clonedElement.remove();
+                  cloneScope.$destroy();
+                }
+
+                // Empty the row and append the new element
+                $elm.empty().append(newElm);
+
+                // Save the new cloned element and scope
+                clonedElement = newElm;
+                cloneScope = newScope;
               });
             }
 
@@ -38,18 +53,16 @@
             // If the row's compiled element function changes, we need to replace this element's contents with the new compiled template
             $scope.$watch('row.compiledElementFn', function (newFunc, oldFunc) {
               if (newFunc !== oldFunc) {
-                newFunc($scope, function (clonedElement, scope) {
-                  $elm.empty().append(clonedElement);
-                });
+                compileTemplate();
               }
             });
           },
           post: function($scope, $elm, $attrs, controllers) {
             var uiGridCtrl = controllers[0];
             var containerCtrl = controllers[1];
 
-            //add optional reference to externalScopes function to scope
-            //so it can be retrieved in lower elements
+            // Sdd optional reference to externalScopes function to scope
+            //   so it can be retrieved in lower elements
             $scope.getExternalScopes = uiGridCtrl.getExternalScopes;
           }
         };