[libcalamaresui] Expose just currentIndex

- drop the current and completed roles, and expose only
  the currentIndex. QML can use the QObject property on
  the model, while QWidgets can call internally through
  the model's data() function.
- we don't need to provide role names for this, so drop that bit.
- simplify the delegate code while here.

src/calamares/progresstree/ProgressTreeDelegate.cpp

@@ -85,10 +85,7 @@ ProgressTreeDelegate::paintViewStep( QPainter* painter,
     font.setBold( false );
     painter->setFont( font );
 
-    bool isCurrent = false;
-    isCurrent = index.data( Calamares::ViewManager::ProgressTreeItemCurrentRole ).toBool();
-
-    if ( isCurrent )
+    if ( index.row() == index.data( Calamares::ViewManager::ProgressTreeItemCurrentIndex ).toInt() )
     {
         painter->setPen( Calamares::Branding::instance()->styleString( Calamares::Branding::SidebarTextSelect ) );
         QString textHighlight

src/libcalamaresui/ViewManager.cpp

@@ -561,23 +561,6 @@ ViewManager::data( const QModelIndex& index, int role ) const
         }
     case ProgressTreeItemCurrentIndex:
         return m_currentStep;
-    case ProgressTreeItemCurrentRole:
-        return currentStep() == step;
-    case ProgressTreeItemCompletedRole:
-        // Every step *before* the current step is considered "complete"
-        for ( const auto* otherstep : m_steps )
-        {
-            if ( otherstep == currentStep() )
-            {
-                break;
-            }
-            if ( otherstep == step )
-            {
-                return true;
-            }
-        }
-        // .. and the others (including current) are not.
-        return false;
     default:
         return QVariant();
     }
@@ -594,13 +577,4 @@ ViewManager::rowCount( const QModelIndex& parent ) const
     return m_steps.length();
 }
 
-QHash< int, QByteArray >
-ViewManager::roleNames() const
-{
-    auto h = QAbstractListModel::roleNames();
-    h.insert( ProgressTreeItemCurrentRole, "current" );
-    h.insert( ProgressTreeItemCompletedRole, "completed" );
-    return h;
-}
-
 }  // namespace Calamares

src/libcalamaresui/ViewManager.h

@@ -153,15 +153,11 @@ public:
      */
     enum Role
     {
-        ProgressTreeItemCurrentRole = Qt::UserRole + 11,  ///< Is this the *current* step?
-        ProgressTreeItemCompletedRole = Qt::UserRole + 12,  ///< Are we past this one?
         ProgressTreeItemCurrentIndex = Qt::UserRole + 13  ///< Index (row) of the current step
     };
 
     QVariant data( const QModelIndex& index, int role = Qt::DisplayRole ) const override;
     int rowCount( const QModelIndex& parent = QModelIndex() ) const override;
-
-    QHash< int, QByteArray > roleNames() const override;
 };
 
 }  // namespace Calamares