Do an initial take on the target executor plugin/configuration mechanism

[pettermahlen]

What happens when a target is executed? How is information communicated between targets? What does the framework do, what does the executor need to do?

TODO:

• implement executors up to test execution (four executors/plugins: classpath assembler, source code assembler, compiler, test executor)
• modify framework to make wiring these guys up 'nice'.
• probably pass all information between nodes explicitly, nothing via the file system.