Closes #2602

Closes #2552

How did these get here?

Closes #2536

Closes #2483

The babel extraction process includes translations from node modules. The extraction process creates two directories: `translations/src` and `translations/node_modules`. When generating the file to sync with transifex we only want the messages in the `src` directory.

Closes #2450

Closes #2460

Closes #2402

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

Closes #2410

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)