Visualize progess with colors

To easily view the current status of the download and convert progress, background colors for the bookmark table have been added.

Successfully downloaded and converted videos will be visualized through a slight green tinge, while videos, which had any problems with downloading or converting, will have a slight red tinge.

Further, any non selected videos to process will be marked in grey.

With this, the user can easily see the progress, the status, and does not have to rely only on the log.