Revert "reinstate access to QSettings to store ignored version". Fixed compilation on Windows with Qt 5.1.1. Added an option to disable GUI, this time for both Qt 4 and Qt 5.

The application author, not library, should decide how to store settings. This reverts commit c76d4bc.
This is to fix https://github.com/pypt/fervor/issues/14.
Also, fixed compilation on Windows with Qt 5.1.1. Added an option to disable GUI, this time for both Qt 4 and Qt 5.