chaining for on and off methods in js lib

[kreopt]

It's very convenient and cleaner to chain player events like this: player.on(evt1,cb1).on(evt2,cb2). So another little patch included.

[kreopt]

second commit avoids the situation when players attached to DOM container by specifying node overwrite each other cause string representation of HTMLElement is [object Object]. I'd change this behaviour to get container id to resolve player name.

[noseglid]

It would be nice to have these split into separate PRs.

Also, you must fix the build error (the code style does not follow the project guidelines)

[kreopt]

done

[noseglid]

Thanks for this! :+1: