In visualization creation, make the icons the same width for consistency

Before:

![screen shot 2014-11-07 at 1 49 43 pm](https://cloud.githubusercontent.com/assets/1178348/4960151/c021bfac-66bf-11e4-9672-45edf5948661.png)

After:

![screen shot 2014-11-07 at 1 50 25 pm](https://cloud.githubusercontent.com/assets/1178348/4960152/c038dba6-66bf-11e4-8396-a31411df0219.png)