Reinstate formatting of "note" blocks in specifications

[zimeon]

The IIIF specifications use warning blocks (marked {: .warning} in the source) which appear with a red bar and background, e.g. the "Incompatibility Warning" in https://iiif.io/api/presentation/3.0/#55-annotation-page

The Auth spec uses and alert block (marked {: .alert} in the source) which appears with a yellow bar and background, see https://iiif.io/api/auth/1.0/ before "Introduction"

The Presentation spec uses note blocks (marked {: .note} in the source) which used to appear with a colored bar and background (was it green or yellow?). These blocks are currently not styled in way that makes their meaning clear or calls them out. See:

• "Machine actionable URIs and links for users" in https://iiif.io/api/presentation/3.0/#rights
• "Model Alignment" in https://iiif.io/api/presentation/3.0/#homepage

Possible solutions:

1. Make {: .note} work again
2. Change prezi source to use {: .alert}

[zimeon]

@glenrobson - interested in your thoughts on this

[hadro]

The new theme makes use of Bulma, so it may just be a matter of connecting old properties to the bulma properties: https://bulma.io/documentation/elements/notification/

[hadro]

Made a small tweak that makes {: .note} work again -- see e.g.:

• https://preview.iiif.io/api/fix_note/presentation/3.0/#rights
• https://preview.iiif.io/api/fix_note/presentation/3.0/#homepage

[hadro]

If all looks fine, maybe you all can merge in #2147 while you're still together...