Update scratch-blocks to the latest version 
Updates the scratch_msgs to support many locales.

Update scratch-audio and scratch-vm

Fix 2px error in stage sizing

chore(package): update scratch-paint to version 0.2.0-prerelease.2018…

Initial version of loading or switching language.

Updates to How To Lib for ISTE

Additional menu item for explicitly adding from Library

Changes to language in "File" menu

Various fixes & additions for library assets

Closes #2402

Localize category names in default toolbox

Use Blockly messages for category names in the default toolbox XML to allow the names to be localized from the Msgs table.

* updated locales reducer to include current messages and messagesByLocale (the previous all messages)
* moved locales out of gui
* include locales in the things exported by gui (index.js)

All thumbnail images have been updated. Titles have been edited, How To's have been reordered. Make A Clicker Game, video link was updated.

Backpack 4: adding costumes and sounds from the backpack

Add `?locale=<localecode>` to load in a new langage.
Add `?enable=language` to enable the language selector
Or combine the two: `?enable=language&locale=<localecode>`
Still accepts a hash, but requires that the hash be a sequence of digits.

Added new locales reducer to gui:
- initializes default  react-intl/localeData
- initializes default locale messages for all locales
- default locale is ‘en’ (can be overridden by URL)

Removed dependency on react-intl-redux, added ConnectedIntlProvider (uses correct locale messages from redux based on current locale)

Update scratch-paint to the latest version 

Sharing costumes and sounds to other sprites and the stage

Update scratch vm to include sharing APIs