Add a little Infobox or icon if favorited multiple talks in the same time slot

[ascheman]

From @noctarius on March 17, 2017 7:49

When favoriting talks from the timetable, the slots are obvious but when looking through topic areas I might have a chance to select multiple talks which happen in parallel. Maybe a small infobox would be nice or adding a little yellow exclamation mark to the header and show the info if the user hovers or clicks it :)

Copied from original issue: dukecon/dukecon#35