Component refactor and loading indicator stub

[vdwijngaert]

See #6 and #10.

• I refactored the code to one root component that contains the state and api logic.
• Entities are being passed down as props to the child components (Schedule and LatestPosts)
• I also had a go at improving the resilience of the fetching logic (enabling further enhancements)
• Made it possible to save fetching state, and show a loading indicator based on that
• Added a stub for displaying fetch-related errors.

[vdwijngaert]

Note: it's my first time working with the WordPress implementation of React, hope I did okay.

[iandunn]

Overall it looks good to me 👍

There are a few things I think would help improve it, if there's time.

[iandunn]

I think the native sort() function may be able to replace this.

[vdwijngaert]

I used the original code (by @avillegasn ?). I haven't looked at the internals, maybe something to look into in the future.

[vdwijngaert]

Thanks for the insightful suggestions, @iandunn. Will try to implement these tonight and make sure everything merges.

[vdwijngaert]

Aight, all suggestions are answered and/or implemented. Let's do this :)

Note: I also made some changes to the session logic. In my test environment all sessions were concluded in 2014, so I got a lot of errors when enabling the production environment. Right now, most properties should have proper fallbacks.

Now it displays "TRACK FINISHED" when there is no more session in the "up next" section. Now it shouldn't throw any errors, but we might want to change this to something more robust, or have some state for when all sessions are concluded.

[iandunn]

LGTM :)