Add indicator when task has additional constraint

[GoogleCodeExporter]

It would be helpful to have a visual indicator that a task has an additional 
constraint defined on it.  Perhaps an icon with hover text detailing what the 
constraint is.  Minimally changing the text color of the appropriate date field 
(e.g., Begin Date text) on the affected task would be better than nothing.

Original issue reported on code.google.com by [email protected] on 11 Feb 2015 at 11:34