added scroll up and down events to receiveInteraction hat block

blocks.js

@@ -993,7 +993,9 @@ SyntaxElementMorph.prototype.labelPart = function (spec) {
                     'pressed' : ['pressed'],
                     'dropped' : ['dropped'],
                     'mouse-entered' : ['mouse-entered'],
-                    'mouse-departed' : ['mouse-departed']
+                    'mouse-departed' : ['mouse-departed'],
+                    'scrolled-up' : ['scrolled-up'],
+                    'scrolled-down' : ['scrolled-down']
                 },
                 true // read-only
             );

objects.js

@@ -4827,6 +4827,10 @@ SpriteMorph.prototype.mouseDownLeft = function () {
     return this.receiveUserInteraction('pressed');
 };
 
+SpriteMorph.prototype.mouseScroll = function (y) {
+    return this.receiveUserInteraction('scrolled-' + (y > 0 ? 'up' : 'down'));
+};
+
 SpriteMorph.prototype.receiveUserInteraction = function (interaction) {
     var stage = this.parentThatIsA(StageMorph),
         procs = [],