ui: Move various components into public/lib

- Move slice_details, thread_details, duration.ts, and timestamp.ts
  into public/lib as they are used by plugins.
- Make timestamp/duration format settings available on App/Trace.
- Refactored Timestamp/DurationWidget widgets a little.

Note: These sorts of settings (timestamp/duration format) are begging
for a generic settings infrastructure, similar to flags but with more
more options, but this is out of scope for this CL.

Change-Id: If507c083bff017e17948bbde36418eb7332f896c