Netflix: add the ability to rewind by subs

[Nitrino]

Related #14 (comment)
Netflix returns an error when rewinding through HTML5 video API.

Tricky way:
We can reuse netflix js.
In the chrome debugger we can find the player instance and rewind as follows:

let videoPlayer = netflix.appContext.state.playerApp.getAPI().videoPlayer;
let sessionId = videoPlayer.getAllPlayerSessionIds()[0];
let player = videoPlayer.getVideoPlayerBySessionId(sessionId);
player.seek(100000)

To use this, we need to inject our js in the page and configure the exchange of messages between page and extension

Example: https://github.com/jonnylin13/LongDistance/blob/61777d7970e2cedd3c2c5d36e6f8fb3a19ee66a0/extension/controller.js