clean up the info-banner component

[mansona]

This cleans up the implementation of the info-banner component but when testing this I noticed that we didn't have a design for the info banner at all 🙈

We can probably merge this PR before we do any work for #146 or we could just add some design stuff to this PR. What do you think @MinThaMie ?

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[MinThaMie]

I would fix it in this PR :) Do we have a design for it or should I just make it nice? Do we know what it looked like before?

What do you think about this one:

[github-actions[bot]]

Some tests with 'continue-on-error: true' have failed:

• ember-canary

  • ember-release-no-deprecations
  • ember-beta

  Created by continue-on-error-comment