Preliminary localization (#777)

* localize the block and menu strings in the pen extension
* adds .tx/config to be able to push translations to transifex
* includes format-message to localize strings and extracting them.
* add setLocale function to VM to allow GUI to pass in locale data.
* refresh block definitions when the locale changes.

### Still to be decided
For now just extracting messages from the pen extension into their own file. We’ll need to decide if each category gets its own file, or group all the strings into one resource.

src/engine/runtime.js

@@ -385,6 +385,14 @@ class Runtime extends EventEmitter {
         return 'EXTENSION_ADDED';
     }
 
+    /**
+     * Event name for reporting that blocksInfo was updated.
+     * @const {string}
+     */
+    static get BLOCKSINFO_UPDATE () {
+        return 'BLOCKSINFO_UPDATE';
+    }
+
     /**
      * How rapidly we try to step threads by default, in ms.
      */
@@ -497,6 +505,41 @@ class Runtime extends EventEmitter {
         this.emit(Runtime.EXTENSION_ADDED, categoryInfo.blocks.concat(categoryInfo.menus));
     }
 
+    /**
+     * Reregister the primitives for an extension
+     * @param  {ExtensionInfo} extensionInfo - new info (results of running getInfo)
+     *                                         for an extension
+     * @private
+     */
+    _refreshExtensionPrimitives (extensionInfo) {
+        let extensionBlocks = [];
+        for (const categoryInfo of this._blockInfo) {
+            if (extensionInfo.id === categoryInfo.id) {
+                categoryInfo.blocks = [];
+                categoryInfo.menus = [];
+                for (const menuName in extensionInfo.menus) {
+                    if (extensionInfo.menus.hasOwnProperty(menuName)) {
+                        const menuItems = extensionInfo.menus[menuName];
+                        const convertedMenu = this._buildMenuForScratchBlocks(menuName, menuItems, categoryInfo);
+                        categoryInfo.menus.push(convertedMenu);
+                    }
+                }
+                for (const blockInfo of extensionInfo.blocks) {
+                    const convertedBlock = this._convertForScratchBlocks(blockInfo, categoryInfo);
+                    const opcode = convertedBlock.json.type;
+                    categoryInfo.blocks.push(convertedBlock);
+                    this._primitives[opcode] = convertedBlock.info.func;
+                    if (blockInfo.blockType === BlockType.HAT) {
+                        this._hats[opcode] = {edgeActivated: true}; /** @TODO let extension specify this */
+                    }
+                }
+                extensionBlocks = extensionBlocks.concat(categoryInfo.blocks, categoryInfo.menus);
+            }
+        }
+
+        this.emit(Runtime.BLOCKSINFO_UPDATE, extensionBlocks);
+    }
+
     /**
      * Build the scratch-blocks JSON for a menu. Note that scratch-blocks treats menus as a special kind of block.
      * @param {string} menuName - the name of the menu