Add news banner

On occasion, we may want to draw the attention of users to certain recent mimestones, like a listing, or wallet sale, or something. Having a banner on the top of the main site would be a useful way to do this. The banner should be fixed at the very top of the page, and it should be possible to close it with a close button somewhere, although that does not need a huge amount of attention on it. The primary CTA in the banner should be some positive action associated with the message of the banner.

As a first use case, lets have a banner that informs the user about our ongoing one key hardware wallet sale. The CTA would be to learn more by reading this blog post: https://blog.joystream.org/limited-edition-onekey-x-joystream/ .

Another use case would be for example the release of our next major network: Nara.

In each case, there are probably suitable visuals that can be used.