#15 user roles

[Hans Saelens]

It would be nice to have a different role for users depending
on the project.

I could be a tester for one project (only being able to enter
issues) and a developer on another project (so people could
assign issue to me on that project).
For other projects I could be a planner, and only allowed to
look at the issues and change priorities and due dates.

This could replace or complement the group concept.