Goodbye monorepo, hello Netlify

[jonearley]

Removed Lerna and the mono-repo structure. This PR has one package: @umich-lib/core.

The DS end user consumes everything through @umich-lib/core so it was making less sense to develop as a mono-repo.

Tooling seems to either support single package repos or mono repos and that has caused a lot of hurdles. The tipping point was Netlify not knowing what todo with a mono-repo. I wanted to add Netlify to have preview builds on PRs (they're working with this change, see below).

Sorry for so many changes in one PR 🙃.

Do we have any concerns with dropping Lerna? cc @bridgetburke, @respinos

[respinos]

@jonearley - Does http://localhost:9000/?path=/story/universal-header--default still work for you?
I am getting Element type is invalid errors.
Same with the fixed chat example.

[jonearley]

@respinos Nope, I get the same error. Not sure why, the UniversalHeader and Chat work when docs are running locally. Docs uses the build lib whereas Storybook uses src, but having Storybook use lib didn't seem to make a difference. Will let you know what I find out!

[respinos]

The console messages were ... well, not helpful but less gibberish:

react-dom.development.js:17117 The above error occurred in the <div> component:
    in div (created by Context.Consumer)
    in LargeScreen
    in div (created by Context.Consumer)
    in HeaderContent
    in div (created by Context.Consumer)
    in Margins
    in header (created by Context.Consumer)
    in HeaderContainer
    in UniversalHeader
    in Example

[jonearley]

@respinos I swept it under the rug with c972b45, but wonder what's really going on.

[jonearley]

Now I'm battling css emotion props not working right...