Pass options to a devtool plugin thru devtool option

[smelukov]

What kind of change does this PR introduce?

A feature that closes this card

Did you add tests for your changes?

Yep

Does this PR introduce a breaking change?

Nope

What needs to be documented once your changes are merged?

About new features of the devtool option

---

After done with it, I will create a PR with these changes to webpack 4 and the docs

[webpack-bot]

For maintainers only:

• [ ] This needs to be documented (issue in webpack/webpack.js.org will be filed when merged)
• [ ] This needs to be backported to webpack 4 (issue will be created when merged)

[webpack-bot]

Thank you for your pull request! The most important CI builds succeeded, we’ll review the pull request soon.

[smelukov]

it complicates for checking the sourcemap option in plugins

@evilebottnawi devtool plugins check the options by the scheme inside of themself