General code cleanup

• Fixed some clazy warnings (don't call first/last() on a temp. container)
• Remove QCoreApplication::flush() calls, they do nothing (empty implementations in both the glib and unix code paths upstream)
• More range for
• Port to QGuiApplication::primaryScreen()
• More PMF signal/slot syntax
• Don't flush an iostream with every iteration through a for loop, just once after the loop should be enough