[keyboard] Re-jig translation extraction

- Use classes to prompt lupdate to extract with a better
  context (e.g. the class name, rather than plain "QObject")
  so that the translation-lookup can use the named context.
- Add hard-coded "default" variant
- Add totally bogus Tajik translations, for testing purposes

src/modules/keyboard/KeyboardLayoutModel.cpp

@@ -20,6 +20,18 @@
 
 static QTranslator* s_kbtranslator = nullptr;
 
+void
+retranslateKeyboardModels()
+{
+    cqDeleter< QTranslator > d{ s_kbtranslator };
+    if ( !s_kbtranslator )
+    {
+        s_kbtranslator = new QTranslator;
+    }
+    d.preserve = CalamaresUtils::loadTranslator( QLocale(), QStringLiteral("kb_"), s_kbtranslator );
+}
+
+
 XKBListModel::XKBListModel( QObject* parent )
     : QAbstractListModel( parent )
 {