Improve UI/UX by aligning checkboxes to the left of the labels.

This is a simple UI / UX improvement that aligns checkboxes to the left of the labels which makes it easier to follow, as well as increasing the margin between them by 5px for better viewability.

The resulting change will look like this:
![spree_clean_cssview](https://f.cloud.github.com/assets/455925/49134/ab0a74a6-5942-11e2-9df0-1907d038da99.png)