Sanitize image url


With Wombat's sample product image: 
`"url": "http://dummyimage.com/600x400/000/fff.jpg&text=Spree T-Shirt"`
I got the error: `bad URI(is not URI?)`
![baduri](https://cloud.githubusercontent.com/assets/5118000/3580437/12c3d92e-0bd6-11e4-8669-4ab200d943ef.png)

This pull request is to avoid special characters and remove trailing whitespaces in product image url