Improve readability and type-safety

Use nullptr instead of 0 or NULL to initialize a null pointer. In some
cases, readability was enhanced by replacing 0 with more meaningful
values according to the type of the pointer being initialized.

src/autotype/AutoType.cpp

@@ -43,7 +43,7 @@ AutoType::AutoType(QObject* parent, bool test)
     : QObject(parent)
     , m_autoTypeDelay(0)
     , m_currentGlobalKey(static_cast<Qt::Key>(0))
-    , m_currentGlobalModifiers(0)
+    , m_currentGlobalModifiers(nullptr)
     , m_pluginLoader(new QPluginLoader(this))
     , m_plugin(nullptr)
     , m_executor(nullptr)