Moved websocket setup logic into a public method.

[rohaanhamid]

Moved websocket setup logic into a public method and added a callback to get notification on successful connection with the Python backend.

Since the websocket setup logic is tied to 'DOMContentLoaded' event, the initialization does not occur if Eel is added later (lazy loading in React for example). This change retains backwards compatibility but allows the websockets to be initialized manually. The oninit callback allows a bit more control for orchestrating creation of components and feedback to user.

[samuelhwilliams]

Hi @rohaanhamid. Sorry for the long delay in getting around to this. It sounds sensible in principle, although I'll need some more time to get my head around the specifics.

The tradition so far has generally been to provide examples for new functionality - would you consider adding an example under examples/? I'll then be happy to look at this more thoroughly.

Thanks!

[samuelhwilliams]

I'm going to close this as it is covered by the proposal in #353 - thanks for the contribution though, and sorry for not pulling it in sooner.