Resolve "unregistered datatype 'QHeaderView'"

Fix #949
When running GR from command line we get:
```
QMetaMethod::invoke: Unable to handle unregistered
datatype 'QHeaderView*'
```
on tab loading. Register the type to fix.

client/main.cpp

@@ -24,6 +24,8 @@
 #include <QApplication>
 #include <QStringList>
 
+#include <QHeaderView>
+
 using namespace GammaRay;
 
 int main(int argc, char **argv)
@@ -43,6 +45,8 @@ int main(int argc, char **argv)
     Translator::loadStandAloneTranslations();
     ClientConnectionManager::init();
 
+    qRegisterMetaType<QHeaderView *>("QHeaderView*");
+
     QUrl serverUrl;
     if (app.arguments().size() == 2) {
         serverUrl = QUrl::fromUserInput(app.arguments().at(1));