[FEATURE] Keep players synchronized

[WesselKroos]

First and foremost, it's a great application and the sync button in itself works perfectly.

Is your feature request related to a problem? Please describe. The players are out of sync after one of these controls have been clicked:

• Fast forward 10 seconds (button or left/right arrow keys)
• Fast forward 1 minute
• Click the pauze/play button
• Dragging/clicking the time slider

Describe the solution you'd like

1. Change the sync button into an on/off toggle.
2. Re-sync the players when the sync button is active and one of the above actions is performed.

[kleepMan]

I can confirm this bug and I also can confirm that the author has fixed this bug with this commit yesterday. There is no new release yet.