- Adding initial support for Write functionality. Units & Transforms mostly. Enums still need work. Needs support for an IsDirty concept so that that every possible attribute isn't written.

- Fixed "#7522 support rotate(angle,cx,cy)". Added new properties and a new constructor overload to   SvgRotate in order to support the optional parameters.
- Removed redundant code from SvgElementFactory.

- Made all transforms (SvgTranslate, SvgMatrix etc) sealed types.