Fix BlackGui header includes

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

refs #598

src/blackgui/editors/form.cpp

@@ -7,7 +7,10 @@
  * contained in the LICENSE file.
  */
 
-#include "form.h"
+#include "blackgui/editors/form.h"
+
+class QWidget;
+namespace BlackMisc { namespace Network { class CAuthenticatedUser; } }
 
 namespace BlackGui
 {