* added precise MeasureString method

- Fixed #7986: public static SvgDocument Open(XmlDocument document) returns null: Implemented the proposed solution
- Added more XML API comments.
- Removed SvgVisualElementEvents.cs class - this was not used and not likely to be used

- Refactored SvgElementFactory to use the new SvgElementAttribute to get available elements.

This was accomplished by adding the new static method to the SvgRenderer class (as detailed in the work item) and a new Draw method overload that takes in a Graphics object as a parameter.

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

- Fixed #6324: SvgElement.PushTransforms and ViewBox - not necessarily related to ViewBox but every   element was 'resetting' the current graphics transform if the element contained it's own transform. This 
  was a very small fix for a large problem (SvgElement.PushTransforms Matrix transformMatrix = new   Matrix(); changed to Matrix transformMatrix = renderer.Transform; in order to inherit the current   transform.)
- Fixed #6344: Parsing document incorrectly parents elements when it encounters empty nodes which are   in a different namespace. Empty nodes are now ignored and current nodes are closed as required. We'll 
  see how this fix goes.
- Fixed #6381: Units in inches are incorrectly parsed as millimeters - problem was caused by some   copy/paste work.
- Graphics has been replaced by SvgRenderer. This is essentially a wrapper around graphics but will allow
  custom svg related properties in the future when needed.
- Removed ISvgRenderer: A concrete implementation is suitable.
- SvgElement.ElementName has been changed to non-virtual and is set by the parser instead of the   developer having to specify it when developing the class.
- Added more XML API documentation.