Separate entity retrieval from jax-rs Response creation

Separate entity retrieval from jax-rs Response creation

- move logic to retrieve entity from db into a separate method
- do not use runner() from AAI core [1][2]
- use global ExceptionHandler to provide a common exception to error response mapping

[1] the runner will spawn a separate thread to process the request. In this change there is nothing to replace this functionality.
The reason that it is removed is that it tightly couples the app with a) aai-common and b) jax-rs and is also catching all exceptions.
Also the timeout mechanism that is implemented is not actually stopping the execution of the thread after the timeout, but rather returning an early response (after 3 minutes(!)).
[2] these changes are also done to make a future full migration to spring boot/the removal of jax-rs easier
Issue-ID: AAI-3693
Change-Id: I177913c5f6295e1cab476e3c206fecacd7620f69
Signed-off-by: Fiete Ostkamp <Fiete.Ostkamp@telekom.de>