Update repo to allow a "platform" to opt for io or html websocket

[kealjones-wk]

Motivation

This repo currently only worked for io based projects meaning that it could not be used in a browser. This project also happens to be the main websocket connection method used by https://github.com/MichaelMarner/dart-redux-remote-devtools which we would like to take advantage of in the browser.

Changes

• Reorganized the files to allow isolation of "dart:html" import
• Added "socket_platform"s that allow users to config which type of WebSocket they would like to use with the Socket class, defaults to dart:io's WebSocket.
• Updated Socket class logic to use globalSocketPlatform in order to allow platform specific logic

This update allows users who would like to use the html based websocket to do so by simply adding:

import 'package:socketcluster_client/src/socket_platform.dart';
import 'package:socketcluster_client/src/socket_platform_http.dart';

and then in main adding:

 globalSocketPlatform = HttpSocketPlatform();

Review

• [ ] Testing on IO based platform to be sure that regressions don't exist for io based consumers (such as flutter)
• [ ] Tests should be added to test globalSocketPlatform usage works as intended
• [ ] Test for Socket Usage when in IO mode and HTML mode should be added

@pauldemarco I would love your feedback on this PR. If you have any issue with its approach please let me know and i would be happy to discuss. My teammates will also be reviewing to double check my work.

[kealjones-wk]

@pauldemarco Just curious if you've seen this yet. :)

[pauldemarco]

I’ll take a look, thanks!

[kealjones-wk]

no rush, i can always just fork this while this is in review, I was just hoping to contribute to everyone's benefit.

[pauldemarco]

This all looks good to me!

[pauldemarco]

Also, love that this is being used in the remote devtools, that's super cool!

[MichaelMarner]

Could this also be published to pub.dev? Latest version is still 0.0.3:

https://pub.dev/packages/socketcluster_client

I can then update the devtools dependency.

Thanks