Improvements to About dialog contributors list

[njx]

1. If the fetch of the contributors from GitHub fails, hide the spinner and show a message below like: "Lots of people (but we can't access GitHub right now to find out who)."
2. _getContributorsInformation() is no longer necessary--you can just replace it with the call to $.getJSON() (since the promise returned by that is exactly the promise you want--the extra promise that _getContributorsInformation() currently returns is redundant now, since all it does is pass through the resolve/reject from the original promise).

[TomMalbran]

Thanks for merging it. I just added some comments to Tuckers request.

1. That looks great as a text.
2. I agree, I separate that part before mainly for the cache, but since is gone, this can be gone too.

[njx]

Looks good, thanks for the quick fix! Closing.

[TomMalbran]

Should this be changed to sprint 21 now?

[njx]

Yup, thanks.