Render list of issues in a release

[str4d]

At the Z|ECC Summit, @AArnott asked how to track which crate release a particular issue might be planned for. This information is available in the DAG: it's the nearest release-tagged node downstream of the issue. However, finding this information in the full DAG can be daunting for people who aren't used to it.

We should render a list view that shows the issues that are directly upstream of a given release, or maybe of all releases in the graph.