[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/Config.cpp

@@ -564,4 +564,5 @@ Config::setConfigurationMap( const QVariantMap& configurationMap )
 void
 Config::retranslate()
 {
+    retranslateKeyboardModels();
 }