added legend service; reworked legend node context management

...p/components/analysis-panel/analysis-panel.component.html

...app/components/analysis-panel/analysis-panel.component.ts

...onents/network/network-legend/network-legend.component.ts

src/app/components/network/network.component.html

src/app/components/network/network.component.ts

src/app/interfaces.ts

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

...pp/services/legend-service/legend-service.service.spec.ts

src/app/services/legend-service/legend-service.service.ts

src/app/services/network-handler/network-handler.service.ts