Small Code/Editor cleanup pass (#4909)

* Clean-up in ConfigGroup

Removed unused templated AddVar and related code.
Replaced legacy types with `AZ::` ones.
Cleaned up cpp file.

Signed-off-by: nemerle <96597+nemerle@users.noreply.github.com>

* Add a few missing Q_OBJECT macros, remove some unused variables.

Signed-off-by: nemerle <96597+nemerle@users.noreply.github.com>

* Apply some of clazy suggestions + simplifications

* removed `emit` from non-signal function calls.
* replaced `QStringLiteral("")` with a constexpr friendly
`QLatin1String()`

Signed-off-by: nemerle <96597+nemerle@users.noreply.github.com>

* Fix a CNewLevelDialog focus bug

Fixed an incorrect QTimer::singleShot invocation.

Signed-off-by: nemerle <96597+nemerle@users.noreply.github.com>

* match lambda to `messageChanged` signature

Signed-off-by: nemerle <96597+nemerle@users.noreply.github.com>

* vs compilation fix + applied review

Signed-off-by: nemerle <96597+nemerle@users.noreply.github.com>

* apply reviewer recommendation

Signed-off-by: nemerle <96597+nemerle@users.noreply.github.com>

Code/Editor/CustomResolutionDlg.h

@@ -12,8 +12,6 @@
 //  Notice     : Refer to ViewportTitleDlg.cpp for a use case.
 
 
-#ifndef CRYINCLUDE_EDITOR_CUSTOMRESOLUTIONDLG_H
-#define CRYINCLUDE_EDITOR_CUSTOMRESOLUTIONDLG_H
 #pragma once
 
 #if !defined(Q_MOC_RUN)
@@ -28,6 +26,7 @@ namespace Ui
 class CCustomResolutionDlg
     : public QDialog
 {
+    Q_OBJECT
 public:
     CCustomResolutionDlg(int w, int h, QWidget* pParent = nullptr);
     ~CCustomResolutionDlg();
@@ -42,5 +41,3 @@ protected:
 
     QScopedPointer<Ui::CustomResolutionDlg> m_ui;
 };
-
-#endif // CRYINCLUDE_EDITOR_CUSTOMRESOLUTIONDLG_H