Add in performance tooling

[pbeshai]

This can be used in the console during dev by typing

Perf.start()

Then doing something, then typing

Perf.stop()

Then using any of these commands to see nicely formatted performance results:

Perf.printInclusive();
Perf.printExclusive();
Perf.printWasted();

Documentation here: https://facebook.github.io/react/docs/perf.html

[pbeshai]

This has revealed that react-select is really slow since it renders all items even when not showing them and it computes reflow unnecessarily often. Also react-bootstrap's Dropdown button is slow too.

[pbeshai]

ping @vlandham

[vlandham]

+1