Show weeknumbers in the calendar / fixed calendar bar for long gantt

[fjhoek]

I would like to add weeks in the calendar bar, this makes planning a lot easier. We often use week numbers.

When we have a lot of projects in the gantt the top calendar bar scrolls away, I managed to put one on the bottom but a fixed calendar would be better.

Furthermore think the class is great! I really like the design and simplicity, most of these gantt charts look bad.