* 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)

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)

* refactor LanguageSelector to reuse MenuBarMenu
* localize aria-labels on MenuBar

Allows the language selection menu to be active if `?enable=language` is in the URL, otherwise shows a ‘coming soon’ tooltip. This can also land on a branch if we don’t want that available on preview.

- language menu opens if the globe is clicked
- language menu closes if mouse is clicked anywhere outside the language selector
- language list is imported from scratch-l10n
- current locale is updated if another language is selected (i.e. the current language selected changes)

Not in this PR:
- styling of language selector
- actually changing the messages!

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

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