Necessary Commit with half-finish GUI

- This commit is pushed to the upstream, so we can check it works
properly with the other classes in this project, because of the
following changes:
- Changed how we "decode" the string, that the client types before
pressing on the following new buttons:
- "Send"
- "Connect"
- "Close"

A new jList is added to the GUI, to show the online users. In the future
it should work together with the Send-button.

- Christopher M.