[libcalamaresui] Give LocaleLabel a default constructor

- Needed for use in containers
 - While here refactor building the english label

src/libcalamaresui/utils/CalamaresUtilsGui.cpp

@@ -262,9 +262,23 @@ clearLayout( QLayout* layout )
     }
 }
 
+LocaleLabel::LocaleLabel()
+    : m_locale( QLocale() )
+{
+    m_localeId = m_locale.name();
+    
+    setLabels( QString(), LabelFormat::IfNeededWithCountry );
+}
+
 LocaleLabel::LocaleLabel( const QString& locale, LabelFormat format )
     : m_locale( LocaleLabel::getLocale( locale ) )
     , m_localeId( locale )
+{
+    setLabels( locale, format );
+}
+
+void
+LocaleLabel::setLabels( const QString& locale, LabelFormat format )
 {
     //: language[name] (country[name])
     QString longFormat = QObject::tr( "%1 (%2)" );
@@ -274,7 +288,7 @@ LocaleLabel::LocaleLabel( const QString& locale, LabelFormat format )
     QString countryName;
 
     if ( languageName.isEmpty() )
-        languageName = QString( QLatin1Literal( "* %1 (%2)" ) ).arg( locale, englishName );
+        languageName = QString( "* %1 (%2)" ).arg( locale, englishName );
 
     bool needsCountryName = ( format == LabelFormat::AlwaysWithCountry ) ||
         (locale.contains( '_' ) && QLocale::countriesForLanguage( m_locale.language() ).count() > 1 );

src/libcalamaresui/utils/CalamaresUtilsGui.h

@@ -140,6 +140,9 @@ public:
     /** @brief Formatting option for label -- add (country) to label. */
     enum class LabelFormat { AlwaysWithCountry, IfNeededWithCountry } ;
 
+    /** @brief Empty locale. This uses the system-default locale. */
+    LocaleLabel();
+    
     /** @brief Construct from a locale name.
      *
      * The @p localeName should be one that Qt recognizes, e.g. en_US or ar_EY.
@@ -192,6 +195,8 @@ public:
     static QLocale getLocale( const QString& localeName );
 
 protected:
+    void setLabels( const QString& name, LabelFormat format );
+    
     QLocale m_locale;
     QString m_localeId;  // the locale identifier, e.g. "en_GB"
     QString m_label;  // the native name of the locale