Added starting time in trajectories so that it can be used as an id

js/client/app-state.js

js/client/views/panels/trajectory-view.js

js/server/direct-data-accessor.js

js/server/main.js

js/server/model/trajectory-model.js

js/server/model/trajectory.js

js/server/nomad-data-accessor.js

js/server/vexp-controller.js