Add basic UserSettings persistence static utility.

Based on localStorage for now.

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;
+        }
+    };
+})();