[FIXED JENKINS-21612] fixed wrong CSS class for f:combobox.

f:combobox is narrow for its CSS class "settings-input" is unavailable. It should be "setting-input".
![editable_combobox](https://f.cloud.github.com/assets/3115961/2059517/640c8d08-8bb6-11e3-83c4-113ff73983a8.png)