Changing background and font color in diagrams

[GoogleCodeExporter]

I spend a lot of time using this great software. All-white Gantt diagram hurts 
eyes after some time.
Please let the user customize the background+alternating+font color on Gantt 
chart (at least).

This issue is a bit related to 
http://code.google.com/p/ganttproject/issues/detail?id=117 but it's a whole 
different user story.

Original issue reported on code.google.com by nehrerj on 16 Mar 2014 at 7:31