add "project group" feature to ease permissions management

all our projects have the same set of permissions, however, we have to implement a distinct permission scheme for each project, because we have "project groups" where only users assigned to that project can edit/schedule/assign/assignable/resolve issues.

this means creating a separate permission scheme for each project, copying another, and removing one set of groups and adding another.

if 'project group' were an option on the Add New Permission page, this would greatly simplify our administration. one way to make this work would be that if project-group were seleted, anyone in a group with the SAME NAME as the project would be given that permission.

alternately, the database structure could be modified to allow assigning one (add fk) or more than one (new table), but this would probably be a lot more work.