Livestream: Paella player integration

To support multiple streams the previous player in the livestream module is to be replaced by the Paella player. Info: https://paellaplayer.upv.es/docs/6.2.x/introduction.html

The implementation includes:

• integration of the Paella player
• configuration of multiple stream URLs (per event)
• configuration of the player layout

The coach can decide which player layout is selected, i.e. how many streams are displayed:

• stream 1 only
• stream 2 only
• both streams side by side

Layout changes are possible at any time during the stream (via course editor).

FX intern:

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