Added undo/redo feature

* new file : HistoryManager.js
* can undo (ctrl-z) and redo (ctrl-y) changes performed through the
tools
* history states are recorded per frame
* a new state is recorder each time a tool is released (introduced
TOOL_RELEASED event for this purpose)
* a duplicated frame doesn't inherit the history states of the original
frame
* there is no limit to the number of states that can be stored per frame
* actions such as creating/duplicating/deleting a frame are not
concerned by this update

js/piskel.js

@@ -79,7 +79,8 @@ $.namespace("pskl");
 
       this.animationController.init();
       this.previewsController.init();
-          
+
+      pskl.HistoryManager.init();
       pskl.NotificationService.init();
       pskl.LocalStorageService.init(frameSheet);
 
@@ -154,7 +155,7 @@ $.namespace("pskl");
 
     setActiveFrame: function(index) {
       activeFrameIndex = index;
-      this.drawingController.frame = frameSheet.getFrameByIndex(index); 
+      this.drawingController.frame = this.getCurrentFrame(); 
     },
 
     setActiveFrameAndRedraw: function(index) {
@@ -176,6 +177,10 @@ $.namespace("pskl");
       return activeFrameIndex;
     },
 
+    getCurrentFrame : function () {
+      return frameSheet.getFrameByIndex(activeFrameIndex);
+    },
+
     initDrawingArea : function() {
         drawingAreaContainer = $('#drawing-canvas-container')[0];
         document.body.addEventListener('mouseup', this.onMouseup.bind(this));
@@ -261,6 +266,8 @@ $.namespace("pskl");
         if(isRightClicked) {
           $.publish(Events.CANVAS_RIGHT_CLICK_RELEASED);
         }
+
+
         isClicked = false;
         isRightClicked = false;
         var spriteCoordinate = this.getSpriteCoordinate(event);
@@ -271,11 +278,11 @@ $.namespace("pskl");
           this.drawingController
         );
 
+
+        $.publish(Events.TOOL_RELEASED);
         // TODO: Remove that when we have the centralized redraw loop
         this.previewsController.createPreviews();
       }
-
-      
     },
 
     onCanvasContextMenu : function (event) {