Add option for sorting most popular sessions

[mariobehling]

The previous eventyay version had the option to show the list of sessions based on popularity.
Provide option to sort sessions by "time", "title" and "popularity"** and implement the following:

• In the specific sort by popularity view remove the in-between time indications similar to how it was done on the previous eventyay version, e.g. here https://eventyay.com/e/55d2a466/schedule?sort=-favourite-count
• On the left side colored area add the info for the date, e.g. Wed 07 Aug
• Ensure the sync between eventyay-talk and eventyay-video works smoothly.