#460 Real interface for coverage

[Matt Chaput]

The current user interface for coverage is very hacky. The user has to manually open the coverage view after running coverage. The UI of the coverage view is very obscure. There is no visible indication how to view coverage information in an editor (double-click file name). Coverage information in the editor is shown using error markers, which is both bad UI and very fragile because as soon as the user edits the file the "fake" errors disappear when it's reparsed.

A real UI for the coverage view and persistent line coloring in editors would be awesome. Possibly see http://www.eclemma.org/ for an example of an Eclipse coverage UI... it looks nice in the screenshots, but I've never used it.