- implements welcome to the preview modal, and unsupported browser modal.
- will need assets updated in Jan.

* Implement GH-830: Add coming soon tooltips

This implements coming soon tooltips for:
* the small stage size
* save, load and language

It also creates the component that can be copied over into the paint editor for use there as well.

Lastly, this does a small refactor on the full screen implementation to include multiple small screen sizes too.

Localizes the pen extension:
- loads all pen locale information - may want to consider dynamically loading locales later.

This way the instance can be reused, which allows access to non-deprecated `DataFormat` and `AssetType`.

Uses new version of scratch-l10n.

* removed anything that was made redundant by scratch-l10n.
* updated a string that wasn’t following conventions
* added .tx/config so developers can start updating Transifex when there are new strings

Alphabetize all the things

  1. Fixed issue with sprites not being dragable when stage zoomed.

  2. Fixed issue with coordinates of mouse position being wrong when
     stage is zoomed. This was caused by the renderer not being
     resized when zooming/unzooming.

  3. Refactored zoom control to separate react component/containter
     with global reducer for isZoomed, which is passed to the stage
     container. This allows for the zoom control to zoom the stage
     menu and stage as seperate containers.

  4. Added icons zoom/unzoom for stage zoom control. Moved icon
     position to be part of stage menu floating to right of start/stop
     buttons.

move all locale data (react-intl/locale-data and gui messages) into locale.js. This also makes switching to an external node package easier because the package just needs to export the same thing as locale.js.

Dynamic import didn’t do what we wanted, so just added `npm run i18n:msgs` to the start command. This is just temporary. Other changes as requested:
* exports in one place
* loc=> locale

Also fixed use of require for localeData to use dynamic import (this one works), so the babelrc changes are needed, otherwise import as a function is not recognized.

Added language-selector component and container. Replaced lib/intl.jsx with reducers/intl.js and added updateIntl to handle language changes.

Moved languages.json into src

Using react-intl-redux package.

This just sets up the default English. Language switching in another PR. Requires locale/messages.json to exist, `{}` is ok.

Thanks @paulkaplan

This reduces the complexity of the reducer, as well as how frequently it's run. The VM will emit a targets update after a step if any target info has changed.

Otherwise it's very annoying to get access to the storage engine to load asset data.