* Fixes the z-index of the prompt so it is behind the quick access panels
* Adds a dismiss `X` button (made sure the click target of this was quite big)
* Change structure of HTML to address template lint issues
* Fix aria-hidden not returning true/false
* Reload current page instead of navigating to / when clicking on the prompt message
Clock manipulation seems not reliable in component tests. This blog post does a great job of explaining it: https://dockyard.com/blog/2018/04/18/bending-time-in-ember-tests
Sadly, we don't have all the "recent" ember test helpers and can't use things like `getSettledState()`.
For now this pattern seems the most reliable and easy to apply, albeit not great.
Note if you wish to reproduce the current timeout, the following command should do it: `QUNIT_SEED=215263717493121190480103670124734840282 rake qunit:test`
This moves the "This site was just updated" modal asking the user if they want to refresh into a subtle prompt that slides down from the header.
Also in this PR I've added a helper to publish message bus messages in JS tests. So instead of this:
```javascript
// Mimic a messagebus message
MessageBus.callbacks
.filterBy("channel", "/global/asset-version")
.map((c) => c.func("somenewversion"));
```
We can have:
```javascript
publishToMessageBus("/global/asset-version", "somenewversion");
```
