AspectCopier must copy xtend/K3 code instead of the generated java code

[dvojtise]

In order to have only one project for the runtime language, the AspectCopier copy only the generated java code from xtend/K3 (probably because this is easier to reuse java code manipulation library and also due to https://github.com/diverse-project/k3/issues/45)

However, copying only the java code prevents K3 from being able to optimize setter/getter code and force the use of inefficient reflexive code (https://github.com/diverse-project/k3/issues/68)

I suggest that the AspectCopier should copy and adapt the K3 code instead of the generated java code.