Fix flickering popover animations

Closes #4138

- Removed JS animation to close in favour of CSS animations
Dude, if it only depends on isOpen, then your `classNameBindings` should
just say `isOpen:fade-in:fade-out` rather than introduce a whole 'nother
variable. What really got me was having to set that variables state in the
open/close methods, whic were already setting state on something else -
just use that something else

On Wed, Sep 24, 2014 at 12:31 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,
>
> I tried moving this into a computed property:
>
>     //Managed the toggle between the fade-in and fade-out classes
>     fadeClass: Ember.computed('closing', 'isOpen', function () {
>         if (this.get('closing')) {
>             return 'fade-out';
>         }
>
>         if (this.get('isOpen')) {
>             return 'fade-in';
>         }
>
>         return 'fade-out';
>     }),
>
> I'd say that it's not worth moving it into that - it's more difficult to
> understand than the current implementation.
>
> —
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> <https://github.com/TryGhost/Ghost/pull/4141/files#r17990638>.
>