Project baseline support

[tiramiseb]

A great feature would be the possibility to set project baseline(s).

(for those who do not know what a baseline is : a baseline is a frozen "picture" of the project at a certain time)

It would allow comparison of the actual tasks status to the originally planned status, in order to measure how the project is evolving.

I've hesitated to submit the issue to the Redmine tracker or here, but I think it could belong here because the original status should preferably be displayed on the Gantt chart, for example with a narrower line in top of the actual status "box", and it doesn't have any impact elsewhere.