Abbreviate the license labels in the statbox

[ctrueden]

Instead of e.g. "GNU General Public License v3+", it should be "GPLv3+".

As part of this, we should implement the TODO in the statbox code to read the license.licenseName (and perhaps license.projectName and license.copyrightOwners, too?) out of the POM. This would give us standard codes from which to derive abbreviated license labels. (Trying to derive it from what people write in <license><name> is likely to drive us mad because people can and do write whatever they want there.)