Add metrics timeline events underneath graphs

We have been discussing adding metrics timeline events underneath graphs for a while now, last in the Metrics timeline workshop in Montreal and on a metrics-team@ mailing list thread. I'm moving that thread here, so that we can keep all open discussion points together in one place and expand the discussion to folks who are not on the team mailing list.

Here are some mockups that I made based on dcf's suggestions:

1. Table with three columns: https://people.torproject.org/~karsten/volatile/metrics-news-mockup-1/userstats-relay-country-table.html

2. One line of text per event (plus one line for links): https://people.torproject.org/~karsten/volatile/metrics-news-mockup-1/userstats-relay-country-text.html

3. Indentation with dates set aside and up to three lines per event for description, tags, and links: https://people.torproject.org/~karsten/volatile/metrics-news-mockup-1/userstats-relay-country-indented.html

Here's some feedback from discussing these mockups with iwakeh at last week's team meeting:

• We might want to rename "Possibly related events" to "Events during this time" or just "Events".
• The third mockup above is most readable.
• Maybe we can add some optional JavaScript magic that only displays the first five entries and that lets the user expand the list if there are more entries.
• Listing entries is all we're planning to do now, though we might add annotations to the graph or even mouseovers in the future.

Some open questions are:

• Are we going to list all events in the displayed timeframe or just the ones that are related to the displayed country, (pluggable) transport, IP version, or server type (relay or bridge)?
• We are adding this list only to the graphs in the Users category, because the metrics timeline focuses on those graphs, too, right?
• Should entries be listed in descending order, like on the News page, or in ascending order?