Improve highlight performance in table listings

[Nicklas Nordborg]

For lists with a lot of rows there is often a lag between the moving mouse and the table row that is highlighted. It can be a bit distracting. If possible, the CSS rules should be optimized to cause minimal lag. One thing to check is for example differences in border settings since that is a known performance hog.

[Nicklas Nordborg]

(In [6067]) Fixes #1701: Improve highlight performance in table listings

Using a transition effect that delays the highlight for a short time makes it feel a lot better when moving the mouse fast. There is still some indication that mouse is moving and there is not much lag. Once the mouse stops the real highlight effect is visible. This only works in Firefox (and Chrome) so there is no improvement in Internet Explorer.