Load options on the first open of the Async drop down menu

Solution demo: https://codesandbox.io/s/o51yw14l59

I used the Async options loaded externally section from the react-select repo.

We start by loading the options on the Select's onFocus and also set the state to isLoading: true. When we receive the options we save them in the state and render them in the options.

I also keep track of optionsLoaded so that only on the first focus do we trigger the call to get options.