[Feature request] % of completion in Gantt charts (was closed in #540)

[CapitanPrimate]

As suggested in #540, sometimes it is required to show the advance of a task in a Gantt chart.

Therefore, it would be useful to be able to specify the % of completion of a task, and show it in its bar. The bar should be split in two parts (complete and pending) and the user should be able to specify the color of each part. Here goes an example:

This probably might be possible using some CSS trick, but it would require the generation of a SVG file, then apply the CSS trick, and then converting it to a raster format, which would be rather inconvenient.

Thanks in advance.