Replace applescript with browser-launcher2

This allows...

1. launching Chrome on platforms other than OS X
2. users to launch their own instance of Chrome (e.g. via command line)
   rather than being forced to use the default instance (i.e.
   `tell application "Chrome"` always used the default instance)

`isDebuggerConnected()` addresses the problem in facebook#510 where the dev tools
would only open once per server session.

Add a '--dangerouslyDisableChromeDebuggerWebSecurity' flag to
packager.js to enable Chrome '--disable-web-security' flag.

This allows users to inspect network requests in Chrome by commenting
the xhr polyfill in InitializeJavaScriptAppEngine.js:
  facebook#934 (comment)

Usage:

    node packager.js --dangerouslyDisableChromeDebuggerWebSecurity

or:

    packager.sh --dangerouslyDisableChromeDebuggerWebSecurity

packager/packager.js

@@ -65,6 +65,9 @@ var options = parseCommandLine([{
   type: 'string',
   default: require.resolve('./transformer.js'),
   description: 'Specify a custom transformer to be used (absolute path)'
+}, {
+  command: 'dangerouslyDisableChromeDebuggerWebSecurity',
+  description: 'Disable the Chrome debugger\'s same-origin policy'
 }]);
 
 if (options.projectRoots) {
@@ -199,6 +202,10 @@ function getDevToolsLauncher(options) {
         return;
       }
       var debuggerURL = 'http://localhost:' + options.port + '/debugger-ui';
+      var chromeOptions =
+        options.dangerouslyDisableChromeDebuggerWebSecurity ?
+          ['--disable-web-security'] :
+          [];
       console.log('Launching Dev Tools...');
       launcher(function(err, launch) {
         if (err) {
@@ -207,6 +214,7 @@ function getDevToolsLauncher(options) {
         }
         launch(debuggerURL, {
           browser: 'chrome',
+          options: chromeOptions,
         }, function(err, instance) {
           if (err) {
             console.error('Failed to launch chrome', err);