ThemeKit 1.1.2, support section themes

[henrybarn]

This repo is currently on low maintenance. See README for details

What are you trying to accomplish with this PR?

Upgrades node-themekit to version 1.1.2
Offers support for section themes with ShopifySlateSections plugin.

Things I considered:
SlateSections now checks if the source directory exists making Slate compatible with both section themes and non section themes.
My last PR had removed the --replace functionality accidentally, that's fixed here
My last PR had an issue with an empty SLATE_IGNORE_FILES in .env, that's fixed here

Please provide a link to the associated GitHub issue.
#1057
#1054

Checklist

For contributors:

• I have updated the docs to reflect these changes, if applicable.

For maintainers:

• I have 🎩'd these changes.

[evankford]

@henrybarn Are you interested in forking this repo to help make an unofficial toolkit for this? I can be involved, though I'm not the most experienced at all of this, I've built about 100 stores on Slate and would like to have an option moving forward.

[henrybarn]

@evankford
I'm hopeful for what Shopify might put out in the future for us. I also don't yet know everything sections everywhere will change or how compatible this theming method will be with the new updates. For my needs in the meantime, I've forked this repo here: https://github.com/henrybarn/slate

And I've made the following upgrades:

• Removed Slate analytics
• Upgrade packages to current
• Includes support from new frame, pages, and content directories
• Upgrade to Babel 7
• References a new slate-starter-theme

You're welcome to give it a try. You will need to update all babel plugins. You'll need node >= 11.10.1

You'll also to have to upgrade the following devDependencies in your slate project's root directory either with the CLI or by editing package.json.

Package name	New version/ref
@shopify/slate-tools	"https://github.com/henrybarn/slate.git"
babel-preset-shopify	"21.0.0"
eslint-plugin-shopify	"^35.0.0"
stylelint-config-prettier	"^8.0.1"
stylelint-config-shopify	"^7.4.0"
@babel/plugin-transform-async-to-generator	"^7.8.3"
@babel/plugin-transform-runtime	"^7.8.3"

And you'll have to use a Babel 7 compatible .babelrc feel free to copy this one which is based on the original .babelrc from slate-starter-theme.

{
  "presets": [
    [
      "babel-preset-shopify/web",
      {
        "corejs": 3
      }
    ]
  ],
  "plugins": [
    "@babel/plugin-transform-async-to-generator",
    "@babel/plugin-transform-runtime"
  ]
}