Feature: implement a popup with options and other informations (superset of #25)

[blmage]

Some features worth considering (see #25 for options):

• provide a summary of the current practice session (all the listening / translation challenges encountered so far with their statements, results, and lists of solutions)
• provide a link to the options page
• provide a link to a debugging page (containing the logs for the current session)
• anything else?