Fix flickering popover animations

Closes #4138

- Removed JS animation to close in favour of CSS animations
Doesn't that mean it's just "fade-out" when closing? o.O

On Wed, Sep 24, 2014 at 1:03 PM, Fabian Becker <notifications@github.com>
wrote:

> In core/client/components/gh-popover.js:
>
> >      name: null,
> >      closeOnClick: false,
> >      //Helps track the user re-opening the menu while it's fading out.
> >      closing: false,
> > +    //Helps track whether the popover is open or closes, or in a transition to either
> > +    isOpen: false,
> > +    //Managed the toggle between the fade-in and fade-out classes
> > +    swapFadeAnimation: false,
>
> @novaugust <https://github.com/novaugust> It does not depend only on
> isOpen.
>
> It is fade-in when isOpen is set to true, it is fade-out when closing is
> set to true (while isOpen is still true) and will remain fade-out when
> closing and isOpen is set to false.
>
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> <https://github.com/TryGhost/Ghost/pull/4141/files#r17992935>.
>