Fix oscillating selection in dropdown menus. Tracker issue 7897.

Fixes [bug 7897](http://tracker.modx.com/issues/7897).

The select elements in a dropdown list get a 1px border applied on hover, meaning if you hover near a boundary between two menu items, the selection jumps back and forth annoyingly.  This removes the border and replaces it with an extra 1px padding on all items, regardless of hover state.

Also removes trailing whitespace in the changed files.