fix : reduce piskel model size

+ moved Serializer and Deserializer to utils.serialization package
+ put all backward code in utils.serialization.backward
+ added static method on Deserializer to make its usage similar to other
  utils in the package
- still not happy with the names used in Deserializer classes
  (deserializer.deserialize ...)

js/utils/serialization/backward/Deserializer_v1.js

@@ -0,0 +1,36 @@
+(function () {
+  var ns = $.namespace('pskl.utils.serialization.backward');
+
+  ns.Deserializer_v1 = function (data, callback) {
+    this.callback_ = callback;
+    this.data_ = data;
+  };
+
+  ns.Deserializer_v1.prototype.deserialize = function () {
+    var piskelData = this.data_.piskel;
+    var piskel = new pskl.model.Piskel(piskelData.width, piskelData.height);
+
+    piskelData.layers.forEach(function (serializedLayer) {
+      var layer = this.deserializeLayer(serializedLayer);
+      piskel.addLayer(layer);
+    }.bind(this));
+
+    this.callback_(piskel);
+  };
+
+  ns.Deserializer_v1.prototype.deserializeLayer = function (layerString) {
+    var layerData = JSON.parse(layerString);
+    var layer = new pskl.model.Layer(layerData.name);
+    layerData.frames.forEach(function (serializedFrame) {
+      var frame = this.deserializeFrame(serializedFrame);
+      layer.addFrame(frame);
+    }.bind(this));
+
+    return layer;
+  };
+
+  ns.Deserializer_v1.prototype.deserializeFrame = function (frameString) {
+    var framePixelGrid = JSON.parse(frameString);
+    return pskl.model.Frame.fromPixelGrid(framePixelGrid);
+  };
+})();