vector2d and quaternion property assigment is broken

Per the documentation, `property vector2d foo: "1,2"` and `property quaternion bar: "1,2,3,4"` should work:
http://doc.qt.io/qt-5/qml-vector2d.html
http://doc.qt.io/qt-5/qml-quaternion.html

Instead, those return `Invalid property assignment: unsupported type "QVector2D"` and `Invalid property assignment: unsupported type "QQuaternion"` respectively.

All the other types, including vector3d and vector4d, work fine (except for matrix4x4, which doesn't have documented assigment from a string).