Remove small padding at the bottom of the image

Not sure if the `display: inline-block` is needed for something else, but it's causing a small padding at the bottom of the image:

![screen shot 2014-06-29 at 16 11 01](https://cloud.githubusercontent.com/assets/408035/3423444/448c206a-ff97-11e3-9fcb-7c5af35d9fe0.png)

In the previewbutton element the padding is more noticeable due to the widget borders:

![screen shot 2014-06-29 at 16 13 30](https://cloud.githubusercontent.com/assets/408035/3423458/9bb1d560-ff97-11e3-9e17-dd959ed900f9.png)