InstantMessagingProgram.Server.java Created

The respective class is all finished, but not tested yet.
Test, New Package, Two new classes

Tested the Server-Class with the ServerTest - Class.
Renamed the InstantMessagingProgram to InstantMessagingProgram_Server.

Created new package for the client:
InstantMessagingProgram_Client with two classes:
- Client.java
- ClientTest.java.
- Created Fields in Client.java
- Created main() in ClientTest.java