Remove MDC adapter and add MDC wrapping to TraceeBackend itself

This PR fixes some small shortcomings:
* TraceeBackend is implementing the `Map`-Interface but we can't get all necessary informations directly from MDC. So we've writen alot gluecode, to satisfy the interface spec.
* There is an independend MDC-Wrapper and an independend Logger-Wrapper that is wired together to an independent TraceeBackend - yes, a muddle ...
* The logic to simulate missing MDC features is located in the MDCwrapper and in the TraceeBackend - not at a central point.

With this PR the TraceeBackend isn't implementing the `Map` interface anymore. Only needed methods are offered -  and an additional "copyToMap"-method. Every specific TraceeBackend is wrapping the MDC itself. So it's a less confusing as before.