Offer summaries of bug listings subtotalled by project/package/assignee/milestone/etc

It would be helpful if I could get a summary of the bugs assigned to me, subtotalled by project or package. Currently the "Package report" <https://launchpad.net/~mpt/+packagebugs> does this for packages only, but this isn't useful for me because none of the bugs assigned to me are in distribution packages. So a minimal fix for this would be to generalize the "Package report" to cover projects and distributions as well.

A more general fix would be a general "Group by:" parameter for bug listings, producing summaries with linked subtotals for whichever unique field you choose -- project/package, assignee, reporter, milestone, importance.

Fixing this would be one way of fixing bug 6074 and bug 87193.