Rename 'finish-launching' event to 'ready',

'finish-launching' is more like a OS X message name, and in atom-shell
it means initialization has done, so 'ready' seems to be a better name
and more easy to remember.

The 'will-finish-launching' event just represents the corresponding
message on OS X and is the same with 'ready' on other platforms, so we
keep its name to indicate that it's only useful for OS X specified
code.

browser/default_app/default_app.js

@@ -17,7 +17,7 @@ app.on('open-url', function(event, url) {
   dialog.showMessageBox({message: url, buttons: ['OK']});
 });
 
-app.on('finish-launching', function() {
+app.on('ready', function() {
   app.commandLine.appendSwitch('js-flags', '--harmony_collections');
 
   mainWindow = new BrowserWindow({ width: 800, height: 600 });