Added automatic detection of locale from browser langauge

Sprite3 Save/Load

Got rid of extra Edge x on monitor list

Fix the sprite layout by making the layout code apply to the wrapper

Locale detection function that checks browser setting and lets URL parameter (locale= or lang=) override the browser setting.

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.