Hide spinner controls from port input fields

A bit of CSS hackery to prevent browsers from displaying spinner
controls on thenport input field. The spinbox controls show up on these
fields because their input type is set to number, and in HTML5 that
means display spinbox controls.

Fixes #710

**BEFORE**: With spinbox controls: ![screenshot 2014-12-10 13 30 13](https://cloud.githubusercontent.com/assets/17978/5384751/010fef32-8071-11e4-9fa5-6c5251bad68c.png)

**AFTER**: Without spinbox controls: ![screenshot 2014-12-10 13 30 24](https://cloud.githubusercontent.com/assets/17978/5384750/feb5ee4e-8070-11e4-872b-ac0094de575c.png)