new fields in the "talks" table

needed for Act#16 (teaser description), Act#36 (allow record)
new fields (added by 6926bcc) must be declared here as well
new field for the "talks" table

when "hide_info" is true, show only the "teaser" field
Act#16: hide details when hide_info is true
links to video
flatten the list of attendees
brain fart: that's hide_details, not hide_info
provide chunked_teaser
change the text; provide it for most European languages
Act#35: show talk title inside the page
add lines
fields for the video URLs + allow recording checkbox (Act#36)
hide_details checkbox and teaser field (Act#16)