Various fixes

What's Changed

• Gdml update by @ebrianne in #3
• could we add "copynumber"? by @bingguo1 in #4
• DUNE ND adds elliptical tube by @brettviren in #12
• Fix gdml_solids.xsd with duplicate element description by @ClarkMcGrew in #13
• feature/Add Material Properties by @ClarkMcGrew in #14

New Contributors

• @ebrianne made their first contribution in #3
• @bingguo1 made their first contribution in #4
• @brettviren made their first contribution in #12
• @ClarkMcGrew made their first contribution in #13

Full Changelog: 0.6...0.7