ProjectExplorer: Modernize

* Use override where appropriate
* Use pragma once
* Make more constructors explicit

Change-Id: I2865fe10f288e3de570826058e43b70a0cb4ee37
Reviewed-by: Orgad Shaneh <orgads@gmail.com>

src/plugins/projectexplorer/projectwindow.cpp

@@ -85,10 +85,6 @@ ProjectWindow::ProjectWindow(QWidget *parent)
     showProperties(-1, -1);
 }
 
-ProjectWindow::~ProjectWindow()
-{
-}
-
 void ProjectWindow::aboutToShutdown()
 {
     showProperties(-1, -1);