Add tour-based tutorial feature. (#153)

* Add tour-based tutorial feature.
Cwc files can contain and a step-by-step tutoral in the form of a
Shepherd tour (http://github.hubspot.com/shepherd/docs/welcome/)
in the metadata at tutorial/tour.

Author: adamcarheden

src/addon/message/message.soy

@@ -1,5 +1,5 @@
 /**
- * @fileoverview Message pane template 
+ * @fileoverview Message pane template
  *
  * @license Copyright 2018 The Coding with Chrome Authors.
  *

src/addon/tutorial/tutorial.js

@@ -41,10 +41,11 @@ cwc.fileHandler.FileLoader = function(helper) {
   /** @type {!Array} */
   this.acceptedFiles = [{
     'description': 'All supported files',
-    'extensions': ['cwc', 'txt', 'html', 'htm', 'js', 'coffee', 'py', 'css'],
+    'extensions': ['cwc', 'cwct', 'txt', 'html', 'htm', 'js', 'coffee', 'py',
+      'css'],
   }, {
-    'description': 'Coding with Chrome file (.cwc)',
-    'extensions': ['cwc'],
+    'description': 'Coding with Chrome file (.cwc, .cwct)',
+    'extensions': ['cwc', 'cwct'],
   },
     {'extensions': ['coffee']},
     {'extensions': ['css']},

src/addon/tutorial/tutorial.soy

@@ -23,6 +23,7 @@ goog.provide('cwc.mode.Modder');
 goog.require('cwc.utils.mime.Type');
 goog.require('cwc.mode.Config');
 goog.require('cwc.mode.Type');
+goog.require('cwc.Tutorial');
 goog.require('cwc.utils.Helper');
 goog.require('cwc.utils.Logger');
 
@@ -59,6 +60,9 @@ cwc.mode.Modder = function(helper) {
 
   /** @private {string} */
   this.templatePath_ = '../resources/templates/';
+
+  /** @private {cwc.Tutorial} */
+  this.tutorial_ = null;
 };
 
 
@@ -130,6 +134,12 @@ cwc.mode.Modder.prototype.setMode = function(mode) {
     sidebarInstance.clear();
   }
 
+  // Remove tutorial
+  if (this.tutorial_) {
+    this.tutorial_.clear();
+    this.tutorial_ = null;
+  }
+
   this.log_.info('Initialize mode and decorate UI for', mode, '…');
   this.mode = mode;
   this.modder = modeConfig.getMod(this.helper);
@@ -183,6 +193,10 @@ cwc.mode.Modder.prototype.postMode = function(mode = this.mode) {
     if (fileInstance.hasLibraryFiles()) {
       this.syncLibrary();
     }
+
+    // Enable tutorials
+    this.tutorial_ = new cwc.Tutorial(this.helper);
+    this.tutorial_.render();
   }
 
   // Event Handling