Make animation duration configurable

[nickschot]

Current implementation has a hardcoded 500ms delay in the JS, similar thing in the CSS. These would preferably be configurable, especially because we can then lower the duration of these notifications in (acceptance) tests as needed.

Ideally we'd also listen for the animationEnd event instead of the current guesstimation in JS.

cc @pichfl

[pichfl]

Touch this issue once I've modernized the service a bit.