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.

Fix:
Now the application make sure to set back the old culture even an error
occurred.
SvgColourConverter.ConvertFrom
SvgPathBuilder.ConvertTo
SvgDocument.Write
SvgExtentions.GetXML

Add:
Attribute: "shape-rendering"

Change:
- Many other properties were unknowingly overloaded. I changed them to
override.
- Some methods or structures need the [CLSCompliant(false)] Attribute.
For example the Enums.TryParse extension. This extension has the where
condition IConvertible. IConvertible is [CLSCompliant(false)] and that
the reason why it is correct to mark the Enums.TryParse extension also
as [CLSCompliant(false)].
- Property "float Opacity" in SvgElement was unknowingly overloaded in
SvgGradientStop as string [stop-opacity]. In the end this property was
only used as float. I changed the SvgGradientStop.Opacity property from
string to float and to override.

Fixed problems when running in multiple threads. The use of a static matrix and the use of StringFormat.GenericTypographic seemed to cause problems when used in multi-threading. This is resolved by making the matrix non static and use a copy of the StringFormat.

Also created a new exception for memory overflows. When using multithreading to render a large amount of big images the bitmap creation can fail (due to memory allocation) throwing an error. This is now caught and a specific exception is thrown.