Support re-initializing the `sendMessage` method used by Remote

[ravenjohn]

xjs only allows setting the sendMessage method on .ready() which means it can only be done once. Since the connection used for sending messages can be replaced. It would be better if xjs allows the sendMessage function to be set again.

xjs.ready({
    remote: {
        type: 'proxy',
        sendMessage: peerConnection.send,
    }
})

Proposed:

xjs.Remote.setSendMessage(peerConnection.send);

Workaround available:

xjs.Remote.sendMessage = peerConnection.send;

[virn]

I'll also be including the method to xjs.Remote.setRemoteType for instances where you need to set the remoteType on the extension to be executed locally, to avoid using the current workaround.

[mikeybanez]

Don't forget to add these changes or additions to the tutorial article about Remote.