Don't start playing item immediately when you are marked as ready

[soredake]

For example i join room before others, i add something to playlist and wait for others to join, but when i marked as ready it starts playing right away even if you are alone in the room. Official syncplay software for desktop for example don't autoplay added items to playlist initially.

[Et0h]

For reference, the official client auto-plays after 3 seconds of all of the following conditions being met:

• There is a file to play
• The minimum users in the room threshold is met (default: 2) and "Play when all ready" is enabled - you can configure/toggle these if you enable "Show auto-play button" under advanced in the menu at the top
• All users in the room are ready (or, more precisely, none are marked as 'not ready' -the distinction is only relevant if a client doesn't support the readiness feature)
• Everyone in the room is playing the same file (i.e. if there are no filename, duration or file size mismatches)

[yuroyami]

Both mpv and exo play the media once it's loaded, by default. This behavior is changed in v0.13.0. However, other readiness-related behavior stuff will be incorporated later