Use Webpack to generate the whole playground

The previous configuration mixed Webpack output with static content in
order to create the playground. This change moves that static content
from `/playground/` into `/src/playground/` and adds a Webpack rule to
copy it into the playground as part of the build.

On the surface this might seem unnecessary, but it provides at least two
benefits:
- It's no longer possible to accidentally load stale build output
  through `webpack-dev-server` in the event of a misconfiguration. This
  was very easy in the previous configuration, and might in fact be the
  only way that `webpack-dev-server` ever worked for this repository.
- It's simpler to ensure that various rules apply to the hand-authored
  content and not build outputs. This includes lint rules, `.gitignore`,
  IDE symbol search paths, etc.

.gitignore

@@ -14,10 +14,4 @@ npm-*
 
 # Build
 /dist
-/playground/assets
-/playground/media
-/playground/scratch-vm.js
-/playground/scratch-vm.js.map
-/playground/vendor.js
-/playground/vendor.js.map
-/playground/zenburn.css
+/playground

src/playground/playground.js

@@ -1,4 +1,3 @@
-
 var loadProject = function () {
     var id = location.hash.substring(1);
     if (id.length < 1 || !isFinite(id)) {
@@ -83,7 +82,7 @@ window.onload = function() {
     var threadexplorer = document.getElementById('threadexplorer');
     var cachedThreadJSON = '';
     var updateThreadExplorer = function (newJSON) {
-        if (newJSON != cachedThreadJSON) {
+        if (newJSON !== cachedThreadJSON) {
             cachedThreadJSON = newJSON;
             threadexplorer.innerHTML = cachedThreadJSON;
             window.hljs.highlightBlock(threadexplorer);
@@ -125,7 +124,7 @@ window.onload = function() {
             var targetOption = document.createElement('option');
             targetOption.setAttribute('value', data.targetList[i].id);
             // If target id matches editingTarget id, select it.
-            if (data.targetList[i].id == data.editingTarget) {
+            if (data.targetList[i].id === data.editingTarget) {
                 targetOption.setAttribute('selected', 'selected');
             }
             targetOption.appendChild(
@@ -213,7 +212,7 @@ window.onload = function() {
     // Feed keyboard events as VM I/O events.
     document.addEventListener('keydown', function (e) {
         // Don't capture keys intended for Blockly inputs.
-        if (e.target != document && e.target != document.body) {
+        if (e.target !== document && e.target !== document.body) {
             return;
         }
         window.vm.postIOData('keyboard', {
@@ -230,7 +229,7 @@ window.onload = function() {
             isDown: false
         });
         // E.g., prevent scroll.
-        if (e.target != document && e.target != document.body) {
+        if (e.target !== document && e.target !== document.body) {
             e.preventDefault();
         }
     });

webpack.config.js

@@ -5,7 +5,7 @@ var webpack = require('webpack');
 
 var base = {
     devServer: {
-        contentBase: path.resolve(__dirname, 'playground'),
+        contentBase: false,
         host: '0.0.0.0',
         port: process.env.PORT || 8073
     },
@@ -108,6 +108,8 @@ module.exports = [
                 to: 'media'
             }, {
                 from: 'node_modules/highlightjs/styles/zenburn.css'
+            }, {
+                from: 'src/playground'
             }])
         ])
     })