CR/NEED - Add Google Analytics support

Popupstore can inject Google Analytics in the layout. You can set the main GA account settings in the config file within config/application. Screenshot:

![screen shot 2013-07-17 at 3 00 59 pm](https://f.cloud.github.com/assets/539188/814370/c2b7a1a6-ef14-11e2-9181-060253e1ae5c.png)

This is using the vendor package SlmGoogleAnalytics which has been forked and modified.

https://github.com/canvaspop/SlmGoogleAnalytics/tree/53151109/add_google_analytics_support

The modifications of the repo allow us to set additional Google Analytics accounts at the controller.

An example was added: http://local.popupstore/checkout

I also updated the README of the repo to reflect the new features.

Let me know if you need more information about the repo and I will add it to the description.

Soyez gentil!