Add basic UserSettings persistence static utility.

Based on localStorage for now.

index.html

@@ -130,6 +130,7 @@
   <script src="js/utils/core.js"></script>
   <script src="js/utils/PixelUtils.js"></script>
   <script src="js/utils/CanvasUtils.js"></script>
+  <script src="js/utils/UserSettings.js"></script>
   <script src="js/lib/jsColor_1_4_0/jscolor.js"></script>
 
   <!-- Application libraries-->

js/controller/SettingsController.js

@@ -21,6 +21,9 @@
      */
     ns.SettingsController.prototype.init = function() {
 
+    	var show_grid = pskl.UserSettings.get(pskl.UserSettings.SHOW_GRID);
+        $('#show-grid').prop('checked', show_grid);
+
         // Expand drawer when clicking 'Settings' tab.
         $('#settings').click(function(evt) {
             $('.right-sticky-section').toggleClass('expanded');
@@ -32,6 +35,7 @@
         $('#show-grid').change($.proxy(function(evt) {
             var checked = this.isShowGridChecked_();
             $.publish(Events.GRID_DISPLAY_STATE_CHANGED, [checked]);
+            pskl.UserSettings.set(pskl.UserSettings.SHOW_GRID, checked);
         }, this));
 
         // Handle canvas background changes:

js/utils/UserSettings.js

@@ -0,0 +1,68 @@
+(function () {
+    var ns = $.namespace("pskl");
+
+    ns.UserSettings = {
+
+        SHOW_GRID: 'SHOW_GRID',
+
+        KEY_TO_DEFAULT_VALUE_MAP_ : {
+            'SHOW_GRID' : false
+        },
+
+        /**
+         * @private
+         */
+        cache_: {
+
+        },
+
+        /**
+         * Static method to access a user defined settings value ot its default 
+         * value if not defined yet.
+         */
+        get : function (key) {
+            this.checKeyValidity_(key);
+            if (key in this.cache_) {
+                return cache[key];
+            }
+            return this.get_(key);
+        },
+
+        set : function (key, value) {
+           this.checKeyValidity_(key);
+           this.cache_[key] = value;
+           this.set_(key, value);  
+        },
+
+        /**
+         * @private
+         */
+        get_ : function(key) {
+            var value = window.localStorage[key];
+            if (value === undefined) {
+                value = this.KEY_TO_DEFAULT_VALUE_MAP_[key];
+            }
+            else {
+                var entry = JSON.parse(value);
+                value = entry.jsonValue;
+            }
+            return value;
+        },
+
+        /**
+         * @private
+         */
+        set_ : function(key, value) {
+            var entry = { 'jsonValue': value };
+            window.localStorage[key] = JSON.stringify(entry);
+        },
+
+        checKeyValidity_ : function(key) {
+            if(key in this.KEY_TO_DEFAULT_VALUE_MAP_) {
+                return true;
+            }
+            console.log("UserSettings key <"+ key +"> not find in supported keys.")
+            return false;
+        }
+    };
+})();