Previously, the syntax was incorrect and was not doing anything.
Additionally, it was attempting to set them as externals in the playground
builds, which is incorrect, they need to be included in the playground build.

Files like src/lib/libraries/sprites.json were being used by
packages like scratch-desktop in order to fetch all the library
assets for offline access. We stopped publishing src in #5263 to
stop bloating the dist with copies of src files. Explicitly
exporting the files that are needed by other repos is a better
long-term plan.

The files are now published to dist/libraries/*.json. Once this is
merged those repos that use the src/ path need to change it to e.g.
`require('scratch-gui/dist/libraries/backdrops.json')`

Apparently this is the recommendation for loaders that look at the `browsers` option.

Allows consumers of gui (desktop, android, etc) to rebuild gui with a relative path for static assets. Default is an absolute path as that is what is required for www.

* thumbnails folder: thumbnail images for tutorials (multistep decks and videos). Images should not need translations (avoid text that would need translation in the image)
* steps folder: gif images associated with tutorial steps. Images can be translated. English (default) images have the extension `.en.gif`, other language images should replace the `.en` with the corresponding locale.
* renamed some of the steps files to be more consistent and a bit less redundant
* removed a couple of files that were no longer referenced
* revised webpack config to allow localized step files to be loaded from `/static` on www

This reverts commit 68af0af2, reversing
changes made to 3fe75020.

This reverts commit 512915b7.

Also include babel-core bridge for Jest itself, which depends on Babel 6.

Required by update to babel-loader

Also requires updating babel-preset-react and babel-preset-env to @babel/preset-react and @babel/preset-env

Configure loaders so they operate on individual modules in scratch-*
dependencies.

scratch-gui exports `index.js` instead of just GUI container.

* WIP tips

* WIP first card stack

* WIP use tips reducer to show things to try

* single card deck similar to mask sequence

* collapse option

* Add zoom card

* WIP tips

* Reorganized to redux

* Add zooming to the gifs

* Blue cards + navigation

* Add tips to new nav bar

* Remove blue

* Update design with icons

* deck updates wip

* Updated card decks

* Add videos to libraries

* Update initial card and clicker preview

* Add backdrop to initial card step.

* WIP use vimeo player instead

* New simple spin deck

* Spin around and say hello decks

* Update button and sub-card styles

* Fix "tips" button in menu bar

* Use move cursor

* Fix cursor

* Use same image for deck preview and library

* Fix cursor again

* Update clicker game deck

* Add videos as single-step decks

* Change tips in menu bar to ? icon

* Change “tips” to “how-tos” in library

* Add help icon to cards

* Update deck library images

* Add drag cover for youtube video to prevent catching mouseup

* add a step to spin deck for clicking control

* Blue bar style updates

* Add step pips

* Update clicker game name to run away

* Fix image padding

* Add change color step to spin deck

* Add start sound step to run away deck

* Update say deck to start with adding a sprite

* Remove package lock

* Remove zooming functionality

* Remove unnecassary prototype changes

* Split up rendering of cards into smaller parts

* Use FormattedMessage for all strings

* Automatic lint fixes

* Almost finished with lint errors!

* Fix more lint errors

* Clean up CSS

* Fix webpack config

build in production mode on travis

Use absolute path when building library (production) so assets can be copied to /static in GUI consumer (like scratch-www)

- export image and sounds in dist/static/assets
- rename main export (`scratch-gui.js`, not `index.js`)
- move project-loader-hoc back to lib (VM doesn’t load properly without it)

export Library if `NODE_ENV===‘production’`, otherwise export playground and examples.

Allow intl to be passed in to GUI as a prop (rather than having to be already in the store)