A bit of harmless refactoring

Prefer C++-style over C-style type casting.
Use qApp instead of QApplication/QCoreApplication::instance().
Use explicit QString::fromLatin1()/fromUtf8() where applicable.


git-svn-id: svn://svn.transmissionbt.com/Transmission/trunk@14404 f4695dd4-2c0a-0410-b89c-da849a56a58e