Cosmetic changes to DecayTree configuration

• Use react-bootstrap Cards to contain the DecayTree configuration on the final page
• Disabled node physics and dragging in the vis.js graph
• Render HTML particle names inside the nodes via trick with SVG
  • <SUB> and <SUP> don't seem to be rendered properly ☹
  • Requires replacing human-readable HTML-only entities (e.g. ω) with globally-XML-compatible unicode code-points (e.g. ω)