2.5.0

• #248: Add full support for cmake qt_add_qml_module(), QuickQanava must now be used
  as a static QML module (qml compiler is automatically applied, it look like it is a lot faster...).
• #244: Add scrollbar support to qan::Navigable, better graph view area support.
• #238: Change group layout, add header support in group delegate.
• #228: Add preliminary support for auto tree layouts.