Polish the fortune server/client examples.

- Remove Qt::WindowContextHelpButtonHint.
- Make the server label interactive (enable copy).
- Introduce new connection syntax.
- Remove unneeded member variables.
- Use constructor initialization where appropriate.
- Adapt the layout to fullscreen platforms by wrapping it
  into a QGroupBox.

Change-Id: I6e397ad082f22ba1e99fc5a17440b2be1f9584f6
Reviewed-by: Topi Reiniö <topi.reinio@theqtcompany.com>