Publish component breakdown as part of release notes

In one of the talks by Gavin at the Dublin moot, he was talking about releases LTS etc and one of the things he showed was a breakdown of issues in each release per component.

He produced a little graphic from the the tracker component data which showed a sort of quick summary of areas affected by each Moodle release. It was something that the people in the presentation really liked - so I think it'd be a good thing to add to our standard release notes templates - helps people get a quick idea of where the changes are in each release.