CommunicationThread and Databaseconnections

Notes
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* Communication thread implemented
* Client- Server communication via JSON established
* Client registration added
* Client login added
* Client conversation added
* Database- tables improved
* Access for database added
* Basic dummy Client added

Explicit and important changes
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* New Kind for Login added
* Scope of some Jars changed to runtime
* Evaluation of JSON in Communicationthread added