Profiler: Improve commit "diff" UX

[bvaughn]

When a fiber is selected, stepping through commits will cause changing props/state to flash yellow in the props side panel. It would be nice if fhe right details pane would always (permanently) highlight props/state that are different from the previous commit. I think this would improve the debugging/digesting process.

[bvaughn]

React DevTools has been rewritten and recently launched a new version 4 UI. The source code for this rewrite was done in a separate repository and now lives in the main React repo (github.com/facebook/react).

Because version 4 was a total rewrite, and all issues in this repository are related to the old version 3 of the extension, I am closing all issues in this repository. If you can still reproduce this issue, or believe this feature request is still relevant, please open a new issue in the React repo: https://github.com/facebook/react/issues/new?labels=Component:%20Developer%20Tools