fix shadow on nodes and edges; keep default node and edge group for fallback cases

...p/components/network-legend/network-legend.component.html

...app/components/network-legend/network-legend.component.ts

src/app/config.ts

src/app/main-network.ts

src/app/network-settings.ts

src/app/pages/explorer-page/explorer-page.component.ts

src/index.html