java plugin: Add an early prototype of a Java binding, similar to the Perl plugin.

java plugin: Add an early prototype of a Java binding, similar to the Perl plugin.

It's totally proof-of-concept, but it's possible to dispatch values from
a Java class using the ValueList implementation provided by Doug
MacEachern from Hyperic. The other way around is not yet implemented,
but that's just a matter of time and code. Configuration, notifications,
targets, matches - all that is still missing.

Right now, the code requires JNI version 1.2. Maybe I'll try to
introduce compatibility with JNI 1.1 at a later point, if it's really
useful for somebody.

Signed-off-by: Florian Forster <octo@leeloo.lan.home.verplant.org>