Allow configuration of the effect + fix for losing script

This changeset allows changing the effect in the preferences as the blinking background can be a bit disturbing when sitting next to the screen. Now it's possible to have the text blinking instead of the background.

Also fixed an issue that the script was replaced after the first data was put in the jobs div. As a self-closing div tag is not supported by browsers it automatically absorbed the subsequent script tag in the div. That has been fixed by changing the self-closing div tag in an empty div element.