✨ Overtime management

[aceol]

In many conferences, even if the time is over, the speaker can conclude or answer questions.
It would be useful to show how much extra time has been granted.
This means : once the timer reaches 00:00, it could continue counting up this time : 00:01, 00:02 ...
It should remain clear that the time is hover so I guess we can keep the red background fullscreen, maybe add a "+" sign in front of the time : +01:30 and a text saying something like "time is over".
If the pause feature is already done, I don't think we should be able to pause the extra time. The action should be to stop the counter.
This behavior should be feature flagged, with an entry in the settings.

• I let the pause as is to not add extra code but it could be added to another PR
• Now the settings form is updated with the current settings (i.e if you use ?duration=10s it will be updated in the settings)

‼️ this should be merged after #33

[aceol]

Deployed on https://aceol.github.io/clepsydre/