Update the SVG tool handling of nested and disallowed elements

[ctrufan]

This PR is to address several issues with the SVG tool that can lead to output of SVGs that are noncompliant per the SVG Tiny P/S spec located at http://bimigroup.org/resources/SVG_PS-latest.rnc.txt .

• Minor bugfix related to the use of a single ampersand instead of a double (did not impact compliance/parsing behavior, just caused tool to throw an error in certain use cases)
• The tool looks at the "allowed element list" and then processes/removes disallowed attributes from the allowed elements. It does not remove the elements that are not in the "allowed" list.
• Tool is using a generic list of allowed elements for an SVG Tiny P/S, so potentially allows nesting of elements that shouldn't actually contain each other.

[ctrufan]

Aside from the allowed elements change, previous code usage of single ampersand meant that if ALLOWED_ELEMENTS_NAME.Contains was false, the latter half would still attempt to resolve and throw an exception.