Unify summary paragraphs across all object types

[mukrop]

Currently, the infographics uses caption, explainers have perex and studies have summaary and datasets and surveys have intro. This complicates getting a short summary text for the object.

• Unify the naming to summary.
• Adjust calls to previous names (layouts, header's description field, open graph summary tag, summary text in RSS/Atom feed).
• Adjust all objects in both language repositories.

[mgrabovsky]

I've started working on this.

There doesn't seem to be an unambiguous choice for surveys. Studies and surveys use the intro attribute as a lead (perex in Czech), which is not necessarily the same as a short summary of the content. Moreover, studies use the summary attribute for a sort of "key takeaways" section, so we're going to have to rename it.

Here's a quick overview of the present state in each layout and the proposed changes:

Layout	Old	New
dataset	caption	summary
explainer	perex	summary
infographic	caption	summary
study	caption	summary
study	intro	lead❓
study	summary	key-takeaways❓
survey	caption	summary
survey	intro	lead❓

[mukrop]

Yes, that makes sense. Do proceed that way.