Port KDE's deprecated classes

- Remaining KFileDialog to QFileDialog
- KIntSpinBox and KIntNumInput to QSpinBox
- KTabWidget to QTabWidget
- Use of KPixmapCache to QPixmapCache
- Usage of KComponentData (KGlobal::mainComponent().aboutData) replaced with KAboutData::applicationData()
- include kmenubar.h replaced with QMenuBar