Livestream: integrated user statistic

In the livestream module, a statistic is added to show how many users clicked on the module while the livestream was running.

Important: number of persons is recorded, not the number of node launches

• GUI is extended by a new tab "Statistics", which is only visible for coaches and owners in the course (not for participants)
• a list of past events is displayed in a table (analogous to the upcoming livestreams
• the table is extended by a column in which the number of users is displayed

The data can be read from the OpenOlat Logging table. Since a lot of data is stored in this table, sufficient performance must be guaranteed when querying the data and generating the statistics.

FX intern:

https://office.bexio.com/index.php/pr_project/show/id/173