Display revision information

[sigiesec]

Show the information on the revisions for which coverage data is displayed (hash, date, maybe last commit message). This is particular useful when the selected revision is "latest", but probably also in all other cases.

[marco-c]

This will be pretty useful especially until #525 is fixed.

[marco-c]

You can also figure out what revision is the "latest" by hovering on the last point of the graph on the homepage.