Add redux-devtools-extension to avoid errors in browsers without redux-devtools extension

[frega]

If the client does not have the redux-devtools extension install, they'll probably encounter a "TypeError: Cannot read property 'apply' of undefined" as the window.__REDUX_DEVTOOLS_EXTENSION__ && window.__REDUX_DEVTOOLS_EXTENSION__() in src/index.js evaluates to false and is passed into the compose function.

[spleshka]

Confirm that it works for me and solved my issue when I got the app installed. Thank you @frega.

[justafish]

Thanks! 👍