Upgrade simpl frontend code to depend on react v16

The simpl-react library currently depends react v16.8.2. However, several simpl front end repos still depend on react v15.5.4.

According to the react version 16 release: "With minor exceptions, if your app runs in 15.6 without any warnings, it should work in 16." See: https://reactjs.org/blog/2017/09/26/react-v16.0.html

This ticket covers updating the simpl frontend repos to be depend on react v16:

• upgrade to react 16 simpl-ui-cookiecutter#7
• upgrade to react 16 simpl-calc-ui#12
• upgrade to react 16 simpl-div-ui#12
• upgrade to react 16 simpl-blackjack-ui#21