Core: Refactor handling of "window state" actions out of MainWindow

Currently the actions for fullscreen, minimize and zoom only apply to
the main window, even if a different window is active.
Refactor the handling of these actions into a WindowSupport class, and
use that instead for the main window. In a second step, this will be
used to add the functionality to the corresponding external windows
(e.g. help and editor windows)

Change-Id: Ief2c880f40948c3bb724196d6e0cfe888b8ece89
Reviewed-by: Daniel Teske <daniel.teske@digia.com>

src/plugins/coreplugin/icore.cpp

@@ -28,6 +28,7 @@
 ****************************************************************************/
 
 #include "icore.h"
+#include "windowsupport.h"
 
 #include <app/app_version.h>
 #include <extensionsystem/pluginmanager.h>
@@ -523,6 +524,11 @@ void ICore::removeContextObject(IContext *context)
     m_mainwindow->removeContextObject(context);
 }
 
+void ICore::registerWindow(QWidget *window, const Context &context)
+{
+    new WindowSupport(window, context); // deletes itself when widget is destroyed
+}
+
 void ICore::openFiles(const QStringList &arguments, ICore::OpenFilesFlags flags)
 {
     m_mainwindow->openFiles(arguments, flags);