[partition] Move initLayout logic to object PartitionLayout

- The logic of the method initLayout belongs to the object
  PartitionLayout. Move logic to that object.
- Use a single method initLayout in object PartitionCoreModule.
- Member m_partLayout in object PartitionCoreModule is no longer
  allocated.

src/modules/partition/core/PartitionLayout.h

@@ -62,6 +62,7 @@ public:
     PartitionLayout( const PartitionLayout& layout );
     ~PartitionLayout();
 
+    void init( const QVariantList& config );
     bool addEntry( const QString& mountPoint,
                    const QString& size,
                    const QString& min = QString(),