qt5 compatibility

with this simple patch (QString.toAscii() -> QString.toLatin1() ; <QtGui/QApplication> -> <QApplication>) the codebase is Qt5 compatible. It should remain compatible also with qt4 (not checked).

Thank you for your great work!

i applied the patch here https://bitbucket.org/luca_santini/plug_mustang_v2_bronco

Applied a Qt5 compatibility patch recieved from a user - fixes #43

→ <<cset 40057045db25>>