Integrate target support

* Ease cross device development by introducing 'targets' which
   group build- and runsettings that are valid for this one target

 Most of the kudos for the code review go to dt. Con, thorbjorn,
 ckandler and others did also review parts of this patch.

Reviewed-by: dt

src/plugins/projectexplorer/projectwindow.h

@@ -52,6 +52,7 @@ namespace ProjectExplorer {
 
 class IPropertiesPanel;
 class Project;
+class Target;
 class BuildConfiguration;
 class RunConfiguration;
 
@@ -93,10 +94,13 @@ private slots:
     void aboutToRemoveProject(ProjectExplorer::Project*);
 
 private:
+    void removeCurrentWidget();
+
     DoubleTabWidget *m_tabWidget;
     QWidget *m_noprojectLabel;
     QStackedWidget *m_centralWidget;
-    PanelsWidget *m_panelsWidget;
+    QWidget *m_currentWidget;
+    IPropertiesPanel *m_currentPanel;
     QList<ProjectExplorer::Project *> m_tabIndexToProject;
 };