Fixed Qt3/Qt4 detection in Slackware.

Since in Slackware when both Qt3 at Qt4 are installed the Qt4 path is in QT4DIR while QTDIR contains the path to Qt3 a check has been added to use QT4DIR, if defined.
Added new application settings.

Added largeFontSize and TextAntiAliasing to the settings dialog and the related load/save functions. Corrected a typo in one of the settings name and fixed some default values.
Updated ViewPainter::init() calls since function definition changed (anti-aliasing removed from parameters, now handled directly in ViewPainter::init() )
Changed the ViewPainter::init() parameters.

Removed anti-aliasing from the ViewPainter::init() parameters, now the function check directly the QucsSettings to see whether anti-aliasing should be enabled.
Merge pull request #120 from in3otd/issue_112

Issue 112: add textantialias and antialias property in QucsSettingDialog.