Display progress bar while loading data from remote tools (ABT or Buganizer)

- Mediator forwards data from remote tools to UploadTracesComponent
- If traces are not visualized, store timestamp received from remote tool and apply it later
- Minor refactoring: do not pass Mediator down to TimelineComponent

Fix: b/263047560
Bug: b/260994827
Test: npm run build:all && npm run test:all
Change-Id: Ia8bacc9a84b7b7c27e0ebb19c9675dd65ec5db9b
13 files changed