Add "Briefing Video" button back

V1 had the button to start the Briefing Video right next to the timer, so GMs could get a group into a room, quickly hit that button, and walk away to help another group. The Briefing Video would play, then the timer would auto-start (auto-start feature already complete, thank you!).

Currently GMs must leave the Puzzles tab to go to Videos, and consequently they lose all the hints they have open in Puzzles. This Briefing Video button is the key feature to streamline the use of ERS V2 for us, allowing us to do a full test in our ERs.