[WiP] HMR in a webworker

[yurynix]

This PR contains a:

• bugfix
• new feature
• code refactor
• test update
• typo fix
• metadata update

• Replaces window -> (typeof self !== 'undefined' ? self : this)
• Upgrades loglevelnext to 3.0.0

Motivation / Use-Case

I'm developing an app that is being executed in a webworker, so I don't have a window global available, I set target: 'webworker' in webpack.config and serving the file via webpack-dev-middleware on express.

This is a test branch to see if I can make it work.

• I've replaced all occurrences of window to (typeof self !== 'undefined' ? self : this) via babel plugin, since that's what is used to build the client.
• I've upgraded the dependency loglevelnext to latest version, since the old version has
  a reference to window https://github.com/shellscape/loglevelnext/blob/v1.0.5/dist/loglevelnext.js#L10

Breaking Changes

TBD

Additional Info

[alexander-akait]

@yurynix hi, how you can use webpack-hot-client?

[jsf-clabot]

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