Fix unit test header includes

* Include only what is used
* Use forward declaration when possible
* Sorted includes

refs #598

tests/blackgui/testutils.cpp

@@ -17,6 +17,8 @@
 #include "testutils.h"
 #include "blackgui/guiutility.h"
 
+#include <QtTest>
+
 using namespace BlackGui;
 
 namespace BlackCoreTest