Tweak benchmark setup scripts

[markerikson]

Couple things I noticed using the repo this evening:

• The setup script always tries to reinstall all dependencies every time
• There doesn't seem to be a way to rebuild just one benchmark easily, particularly because the setup script and folder structure involves copying the built benchmark over to multiple folders

It would be helpful if things were split up a bit so that we could:

• Rebuild benchmarks without reinstalling all dependencies
• Rebuild only a single benchmark at a time

I think the "single benchmark build + copy and rename React-Redux files" approach I originally had might make this work better.