Convert to ES5, add web server

* No compilation step
 * Beginnings of web interface
 * Simple express server; React-based frontend
 * CommonJS style across codebase; auto-converts to RequireJS for browser
 * Using diffsync for realtime UI
 * "Provider" -> "Plugin"
 * Plugins expose one or more Providers

lib/version.js

@@ -0,0 +1,12 @@
+var fs = require('fs');
+var path = require('path');
+
+'use strict';
+
+module.exports = getVersion();
+
+function getVersion() {
+  var packageJSONPath = path.join(__dirname, '../package.json');
+  var packageJSON = JSON.parse(fs.readFileSync(packageJSONPath));
+  return packageJSON.version;
+}