Added fadeout to gh-popover

Closes #2868
- Uses jQuery's `.fadeOut` whenever a popover is closed.

Death to the ancient issues!
I think this may be why the tests are failing. If you click the `popover-button` once, and have it open, and then click it twice within 200ms of each other... 

1. First click opens
2. Second click will close in 200ms
3. Third click will close in 200ms (because it's still open) rather than cancelling the fadeOut and stopping the close.

I know I can stop the fadeOut via `$().stop`, but I don't have an idea just yet for "and don't set open to false!" half of it.