Make sockjs optional

[sebakerckhof]

More and more, people might not care about supporting older browsers, or even browsers at all (e.g. react native). This could mean that they only support environments that also support websockets, making sockjs of little value. It would be great if the sockjs code, at least client-side, would get pushed in a separate, optional package so that people that don't need it can do without.

[dr-dimitru]

@sebakerckhof fallback to XHR is always will be required. WebSockets may not work for various reasons due to network configuration, proxies or browser settings.

[mitar]

Why would you not want to include sockjs? Just because of the client code size? Are there any other drawbacks?

[mitar]

To me it is more like a polyfill for websockets.

[StorytellerCZ]

From what I have seen of the code sockjs is loaded only for old browsers and as @mitar has pointed out it acts as a polyfill, so in that aspect it is optional already, or am I missing something here?