Create executable war with Jetty and build num

Side-effects: changed binary name, how port is supplied.

- use Jetty instead of Tomcat (better documented,
  full control over the final MANIFEST.MF)
- use buildnumber-maven-plugin to include git hash and build timestamp in the archive's manifest
- add Main class to run the web app via the embedded jetty (must be copied to the archive's root via antrun)