Debugger: Improve UnstartedAppWatcherDialog.

Make it possible to ESC out of it by using a QDialogButtonBox
and overriding the ESC shortcut. Also remove context help button.

Change-Id: If632c5f3cadc012dd2f67dcb709570f7a9c25bf5
Reviewed-by: David Schulz <david.schulz@theqtcompany.com>

src/plugins/debugger/unstartedappwatcherdialog.h

@@ -64,6 +64,8 @@ public:
     bool continueOnAttach() const;
     void startWatching();
 
+    bool event(QEvent *) override;
+
 signals:
     void processFound();
 
@@ -93,7 +95,6 @@ private:
     QCheckBox *m_hideOnAttachCheckBox;
     QCheckBox *m_continueOnAttachCheckBox;
     QPushButton *m_watchingPushButton;
-    QPushButton *m_closePushButton;
     ProjectExplorer::DeviceProcessItem m_process;
     QTimer m_timer;
 };