Provide more generally useful CKEditor styles

Problem/Motivation

Noticing that sometimes editors tend to format entire paragraphs bold or italic, we also notice that this inflicts accessibility issues.

Resolution

Add CKEditor styles

• span.bold|Bold (faux)
• span.italic|Italic (faux)

This is not automatically educating editors to format copy text screenreader-friendly but at least we provide a possibility.

While we are at it, let's add some more options:

• span.mark|Textmarker to mark parts in a Draft that need rework
• blockquote.callout|Callout extra highlighted blockquote (professional magazine editors like that)
• blockquote.plain|Blockquote simple Blockquote with less visual emphasis to still allow accessible editing
• span.quotee|Quotee quoted person inside a blockquote (yes, figcaption would be appropriate but support is lacking
• a.cta|CtA Link button-like styling for call-to-action links (still different from buttons to avoid confusion)