Corrected and simplified WAR / Jetty configuration:
In contrast to jangaroo-maven-plugin's default, we now compile
directly to the Web app "exploded war" directory. Rationale:
This is what the Jangaroo IDEA Plugin does, anyway, and fast
development turn-around works for both Maven and IDEA.
Downside: Jetty is started with two occurrences of each JAR on
the CLASSPATH, one from the local Maven repository and
one from WEB-INF/lib, but they should be the same after each
mvn install, so we can live with that. Maybe I find out how to
tell Jetty to not add dependencies to the CLASSPATH automatically.