Retro Timer: Wrong time when joining a session while a timer is active

[Nomandes]

Describe the bug
When the moderator has started a timer and a new participtant joins the board, his timer will differ from the other participants.

Technical origin
Bug originates from the fact that the visible timer is calculated from the local variable timerDuration which defines how long the timer already lasts. This value is not communicated to the new participant, so the timer starts at the original set time.

To Reproduce
Steps to reproduce the behavior:

1. Create session with any browser
2. Create a timer of any time
3. Let pass some time
4. Add a new participant
5. See remaining timer at participants board

Expected behavior
The timer of the new participant should be the same as everybody else

Desktop (please complete the following information):

• OS: macOS
• Browser: Arch (Chrome)
• Version: current