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/CustomizeKeyboardDialog.cpp

@@ -211,9 +211,9 @@ public:
 
     void Reset(QAction& action)
     {
-        emit beginResetModel();
+        beginResetModel();
         m_action = &action;
-        emit endResetModel();
+        endResetModel();
     }
 
 private:
@@ -266,7 +266,7 @@ QStringList CustomizeKeyboardDialog::BuildModels(QWidget* parent)
         categories.append(category);
 
         QMenu* menu = menuAction->menu();
-        m_menuActions[category] = GetAllActionsForMenu(menu, QStringLiteral(""));
+        m_menuActions[category] = GetAllActionsForMenu(menu, QString());
     }
 
     return categories;