Speakers block dropdown sometimes hidden

[cjyabraham]

Speakers block uses the react-select component that has an open issue with the z-index of the dropdown and an open PR to fix it. When this gets committed we should update our code to pull in the fix. Problem shown below:

[cjyabraham]

Fixing this appears to be a bit of a whack-a-mole. I believe, however, that the most common case of this issue is when a Speakers block is nested inside of a Group block. The dropdown won't show beyond the limits of the Group block since it is nested inside of it. The fix I've applied corrects for this case. There may be some side-effects of this fix on Group blocks since we're changing the overflow setting on them. If any are found and they pose a problem, we can revert this fix.

There may be other cases where blocks hide a portion of the select drop-down. If we can know about these cases we can work on fixing them as well.

One other case I do know about is when the SEO bar at the bottom of a page blocks the drop-down. I'm not sure how common a problem this may be, how often the Speakers block would reside so low down on a page. If it is a common problem then we can work on a fix for this as well.