Refactor properties

Remove QgsAbstractProperty and subclasses, and instead use a single
QgsProperty class which covers the use of QgsAbstractProperty
and its subclasses. This simplifies the API and avoids pointer
handling. QgsProperty is implicitly shared for memory efficiency
and inexpensive copies.

Author: nyalldawson

python/core/composer/qgscomposerutils.sip

@@ -114,7 +114,7 @@ class QgsComposerUtils
      * @note this method was added in version 3.0
      * @see readDataDefinedPropertyMap
      */
-    static QgsAbstractProperty* readOldDataDefinedProperty( const QgsComposerObject::DataDefinedProperty property, const QDomElement &ddElem ) /Factory/;
+    static QgsProperty readOldDataDefinedProperty( const QgsComposerObject::DataDefinedProperty property, const QDomElement &ddElem );
 
     /** Returns a font where size is set in pixels and the size has been upscaled with FONT_WORKAROUND_SCALE
      * to workaround QT font rendering bugs

python/core/core.sip

@@ -120,6 +120,7 @@
 %Include qgsprojectversion.sip
 %Include qgsproperty.sip
 %Include qgspropertycollection.sip
+%Include qgspropertytransformer.sip
 %Include qgsprovidermetadata.sip
 %Include qgsproviderregistry.sip
 %Include qgspythonrunner.sip