Add information about the build (time, revision, and branch) to jar and war manifests.

In order to address issue #59, I used the `buildnumber-maven-plugin` to determine the time at which the Maven build occurred and the git branch and revision from which the code was built.  That build-related information is included in the `MANIFEST.MF` entry in `jar` and `war` files.  I verified that Maven projects created from the archetypes (`student-archetype`, for instance) still build even though they are not under revision control.