Solved issues

In this pull request I've added some nice things and solved some issues:

* Issue #57 can't be reproduced on my PC. Maybe you have a deprecated php version installed? I'm using **PHP Version 5.5.9**
* Issue #58 can't be reproduced as well. If it has nothing to to with your PHP version, maybe explain what you've done to receive such messages
* Finished issue #56: Implemented logout functionality and menu
* Finished issue #60: Implemented flash messages

Give me some feedback about your PHP version. Thanks!