...after resolving the fundamental design problems,
a policy mix-in can be defined now for a thread that deletes
its own wrapper at the end of the thread-function.
Such a setup would allow for »fire-and-forget« threads, but with
wrapper and ensuring safe allocations. The prominent use case
for such a setup would be the GUI-Thread.
after all this groundwork, implementing the invocation,
capturing and hand-over of results is simple, and the
thread-wrapper classes became fairly understandable.
- relocate some code into a dedicated translation unit to reduce #includes
- actually set the thread-ID (the old implementation had only a TODO at that point)
