SimpleServerClient v2.4.1

I made many improvements suggested by essemX and some I thought of myself:

• Client: removed the auto kill feature
• Client: added a stop mechanism to disconnect
• Client: added constants for default user and group ids
• Client, Server: many code style improvements
• Client, Server: translated many German comments and outputs
• Client, Server: reworked some output and error messages
• Client: reduced printing of exception stack traces
• Client: improved connect-login-circle (not more login attempts without a connection)
• Client: made sendMessage arguments accept all kind of Objects instead of only Strings
• Datapackage: removed redundant implementation of Serializable
  Co-Authored-By: essem essemx@users.noreply.github.com

Also

• added a new catch-clause, so the client will notice if the server forgets to send a reply (sendReply(Socket, Object...)).
• slightly improved Diffie Hellman Factory

SimpleServerClient v2.4.0

• Speed ​​of network operations improved by about 90% on average.
• onClientRemoved could not be overwritten so far, because the visibility of the Server#RemoteClient subclass was private. Changed it to protected.
• Changed many private other modifiers to protected in Client and Server classes to make overwriting easier; also added three new methods returning booleans to the client: isListening(), isConnected() and isServerReachable()