Subject: Splitting Core into even more modules

Current state ...
Maven dependencies a ---> b (a depends on b).

Hope you can see the Left- and Up-arrows ...

LAYER1:    applib <----  appLib-legacy
              ^               ^
              |               |
LAYER2:    metamodel <-- metamodel-legacy
              ^               ^
              |               |
LAYER3:    runtime <---  runtime-legacy


LAYER4:    viewer-wicket-ui (not yet)


It's perfectly safe to move classes around as long as movement stays in
the same layer.

That way we can build everything, and decide what combination to package
for deployment.

I'm moving axon, guava, and reflections now out of applib and provide
following plugin modules as plugins:

* isis/core/plugins/discovery-reflections
* isis/core/plugins/eventbus-axon
* isis/core/plugins/eventbus-guava

Cheers, Andi