Improve [blocks] shortcode to support various use cases

[bobbingwide]

The [blocks] shortcode, developed as part of #61 has multiple uses. We need to extend the ad-hoc usage... where the block type names are passed to the block, to make it easier to create documentation about Transforms, Nested blocks and other stuff.

This issue has been raised to discuss the short and long options.

Short term

• [ ] To use the [blocks] shortcode to reference new, changed or deleted blocks
• [ ] To link to related blocks for Transform
• [ ] To link to related blocks for Nesting
• [ ] Ad hoc linking to an individual block.

The style of the list to be displayed depends on the context.

• Unordered list of links
• Simple ( inline ) list of comma separated links using the block's Title attribute only
• Simple link using the block's Title attribute

Examples

• Paragraph - core/paragraph
• List - core/list

Transforms to: Paragraph, List

More often than not we won't want to display the block's thumbnail. And we don't yet want to display the block's icon since it's not available in the server.

Long term

In the longer term we might be able to automate quite a few of these lists.

• Changes between plugins versions should be detectable
• Transform and nesting information should be available from the block registration.

[bobbingwide]

Note: The simple list of comma separated links can be mostly achieved by CSS styling span.bw_list span.summary { display:none; }