Option to have replay video be muted by default

[fabyeah]

Thanks for this great lib!

For my use case, I need the replay video to be muted by default, as a user might record something with his phone and not want the replay blasting sound right after, but rather have it be muted. Especially since I don't show video controls, so there is no mute button.

I wanted to create a PR, but found that there is some muting and unmuting going on in the code and wasn't entirely sure how to handle that. As there is already a isReplayVideoMuted state var, maybe have a shouldReplayVideoBeMuted attribute (that would be toggled if the user actively mutes/unmutes a video with the video controls)? What do you think?