Unify Scijava and Beaker languages ?

I really don't know if it's a good idea. I only open this issue for discussion and to know what your guys think about that.

From the ImageJ side, we have some very specific needs the way we interpret the source code (I am thinking about the `@Annotations` for example). Saying that some code could probably be shared between both projects.

[Scijava scripting languages](https://github.com/scijava?utf8=%E2%9C%93&q=scripting-*&type=&language=) are now used for years and are pretty stable. By having a JSR-223-compliant base kernel, I think it would be pretty easy for Beaker to use those packages.

What do you think @ctrueden ?