Updated threading tests to use the resource file, updated the file loader in the test helper to be flagged as obsolete and changed the working of the multi-threading fail test since this is not always failing with the error while processing the SVG. If it's not failing now it will be flagged inconclusive.

SvgTextBase Text property setter resets Node collection to have single content node with provided text.

Added a test with a SvgText element where the whole text element was not written to XML of a deep copy of the SvgDocument.

- Changed SvgImage.Href property from Uri type to String to avoid UriFormatException if Uri contains too much data
- Changed GetImage to receive a string instead of Uri object.
  - Created a temp Uri object in method with substring of allowed length and using this to determine Uri characteristics

As long as the functions AdjustForViewBoxWidth and
AdjustForViewBoxHeight are not fully developed pay attention that the
ViewBox width and height will not mismatch the positions of the marker
element then one of them are zero.

This changes are based on Issue #212 from mater.

Add: Quick solution to avoid  ViewBox width or height zero calculation.
Add: UnitTests

Create metafile rendering Unit Test based on Issue #210 from master.

This reverts commit a7097113.

This reverts commit 480a54d8.

Based on Issue #204.
Now users can add customer fonts/ private fonts to
SvgElement.PrivateFonts.

Unit Test:
Add Test: PrivateFontsTest
Add Resources from PrivateFontsTest.
Add SvgTestHelper
Change MultiThreadingTest, now based on SvgTestHelper to use shared code
(no code duplication)

Note:
MuliThreadingTest TestFile is not available. The vvvv/master should add
the test file to the resources or other developer can not test the svg
engine.

- Adding W3C test cases and a test fixture
- Fixed support for CSS stylesheets (particularly when class names are
referenced)
- Refactoring unit calculations so that percentages and fractions
calculate more accurately
- SvgImage:
- Support PreserveAspectRatio attribute
- Support for referencing svg images
- Refactored text rendering to use the AttributeCollection inheritance
scheme
- Initial attempt at 'ex' unit support
- Added support for system color names
- Changed parsing of entities to support XML entities
- Supporting loading of a svg document directly from a XmlDocument with
requiring serializing the document as a string first.
- ...