Filter by Role clause
We are using the roles like "Project manager" and "Tracker manager" who must to assign issues to project's actors and to control the execution flow.
We have in common about 100 projects and one user can have different roles in different projects.
And there is the problem for project manager to find "All unassigned issues in all managed projects".
So this patch introduces a new filter clause "Role" which means "the role of the logged user in the project".