* feat: initial implementation of banner component.
* feat: add props description.
* refactor: Change the way banner is structured.
* refactor: small refactor of banner component and example.
* refactor: remove some not needed logic from banner and add example.
* refactor: refactor of banner props description and little clean up in component.
* refactor: simplify implementation of banner
* feat: add snapshot tests for banner.
* feat: add banner gif.
* fix: fix example.
* fix: reduce banner gif size.
* fix: reduce gif size even more.
<!-- Please provide enough information so that others can review your pull request. -->
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### Motivation
<!-- What existing problem does the pull request solve? Can you solve the issue with a different approach? -->
### Test plan
<!-- List the steps with which we can test this change. Provide screenshots if this changes anything visual. -->
Currently, we wrap certain components such as FAB.Group and Snackbar in Portal by default.
This means they are always rendered on top of everything and there's no way to control it.
This makes it hard to integrate with navigation libraries such as React Navigation.
The PR removes the Portal wrapper by default and exports PortalHost so users can control where the components are rendered.
In future React Navigation could provide an API to render things on top of the screen and users would be able to take advantage of it.
### Motivation
The ref function is called twice on updates (see https://reactjs.org/docs/refs-and-the-dom.html#caveats-with-callback-refs). This behaviour causes the variable `this._manager` sometimes to be null during rendering and in that case actions are pushed to the queue again. Since the queue is only processed once (during componentDidMount), somes changes will never be visible. The simple solution is to bind the ref-function as mentioned in the link above.
### Test plan
Dynamically change `visible` parameter of Modal. The Modal won't be visible on the second time.
