add to the statistics

[bansp]

These are the orphan ideas transferred from ticket #67 and concerning ideas for what statistics we can compute and visualise:

• group by format family, display the number of occurrences of each format (by format ID!), as provided in the recommendation files, and sorted alphabetically
  • note that we have a "hidden page" on format families (and just keep forgetting about it!): https://clarin.ids-mannheim.de/standards/views/format-families.xq (thanks, Eliza!) see also ticket cross-format categorizations (keywords, <formatFamily>) #129
• The number of recommendations and recommendations per domain
• Also the number of <centre> elements with some attributes, like, @ri, @status, etc.

Let's add to this indiscriminately and then see if anything is worth keeping.

[bansp]

"for this format, which domains are the most popular?"

[bansp]

See also ticket #240