Wrap cformat-ed strings to get the correct len() etc.
Select all registrants by default & progress bars

 - When trying to show stats without any registrants selected, attempt to
   select all of them by default instead of showing an error. (The error is
   still shown if there are no registrants to select from.)
 - Fix `i-box` to handle both `horiz` and `vert` layouts at the same time.
 - Add sparkline progress bars `i-progress`.
Add new social events stats

 - Add new and prettier social event stats with billing details
badges & red/green pastel colors

 - added classes to display "badges" with some info
 - new pastel colors in plaette for red and green
 - tweaks to progress bars
 - updates imports for partials to reflect the above changes
Add new stats tabs for conference registrants

 - replaced old show stats buttons in the registrants list by a tab
 - new improved stats: overview, accommodation, sessions, social events
 - "indico_" prefix now optional when include JS packages (in WPBase)
 - removed old stats computation from WP class
 - new stats classes ot aggregate the data
 - use Jinja to render the stats
Small fixes
Post wip changes