Correcting Cart Template Class Names

Following up #4600 we decided to add class names to the cart meta data. I'm further updating this by adding some sanitization for class names that might be more than one word which were adding spaces in the class names.

![cart___woocommerce_github-2](https://f.cloud.github.com/assets/1065372/2252191/4708b294-9da5-11e3-89b2-6ba2e1465351.png)

From: https://woothemes.zendesk.com/agent/#/tickets/149704