Nested animated containers can cause the child container to ghost

[brettburley]

When you have two nested animated containers, if the child container is animated first, when the parent container is animated using the explode transition (which copies the dom), the child container is visible in its non-animating state.

Here's a sample reproduction:
https://ember-twiddle.com/372496292a0f4d6fd862c40ba700ca93?openFiles=templates.application.hbs%2C

It appears that this is a result of applying visibility: visible in animate, and children that are visible: visible inside of a parent visibility: hidden are always visible.

[brettburley]

Resolved by #607.