Do not create a new Thread in a new ThreadGroup when performing an execution.

[XerTheSquirrel]

To handle the profiler profiling only a given execution I had to create a new ThreadGroup and spawn a new thread for every invocation that occurs. This creates some overhead so I am very much in the idea that this should be reversed and instead having a thread monitor of sorts or attachment. This should decrease latency and allow executions to perform faster. As a result the profiler will not have a good idea of which threads belong to a given execution if they are unflagged, but this might not be too much of an issue since the information might be wanted anyway.

This is related to #77.