Fix layout issue for associations in edit forms

The add and edit buttons next to association selects are given the inline style 'float:left;margin-left:10px', but the select box has no float and 'display:inline-block' - so, instead of appearing to the right of the select box, the buttons appear on the left w/ a weird margin.

![bug](https://f.cloud.github.com/assets/533045/81582/72d6ff92-6341-11e2-820b-22c2d4960e30.png)