Add new version alert

[ehne]

Probably should let the user know if there is a new feature or patch version. So that they can download the new version and get whatever fix.

Proposed solution

Check on the localhost ui, and put a banner up if there is a new version. Probably reuse some of the code from the gh-pages branch, and how the docs have the version switcher.

In terms of sending the installed version of PyNode Next to the client, just dispatch an event when the user connects to the socket. (through self.canvas.onmessage or something like that)

version_dispatch_dict = {'isPyNodeNext': True, 'type': 'version', 'message': 'v1.9.1'}
self.canvas.onmessage('getPyNodeNextVersion', lambda: self.canvas.dispatch(version_dispatch_dict))

let socket = initSocket(function() { 
  canvas.message('getPyNodeNextVersion') 
}, dispatch);

And then just grab the message in the js dispatch function and handle it.

[ehne]

Should be closed by 88c03d9 when it is merged.