Add a meta tag to make sure google doesn’t try to autotranslate:
https://support.google.com/webmasters/answer/79812?hl=en

The initial commit for this was before we hooked up the community to redux.

And implement toggle on player playground

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)

There will probably need to be more backpack config options in the future, so just make this a bit more future proof

Since compatibility-testing got switched to use the player mode, it doesn’t need any of the stage/controls components.

* Export initial states for each reducer
* combine all gui reducers (excludes scratchPaint and intl)
* combine all initial states to create default guiState for preloading in www
* expect all of the gui state to be accessible at `state.scratchGui`

GUI will export a reducer to be included in the enclosing component’s redux when GUI is used as a library. The app-state-hoc is moved into the playground examples to provide a store when GUI is being used stand-alone.

The project loader that is exported with GUI just expects to be passed projectId as a prop, and it manages loading project data.

The part of the project loader that watches for URL hash changes for the playground is a new HOC that is only used in the various playground examples.

Fixes #1853

* Player mode

Add isPlayerOnly property on GUI. Move isFullScreen into mode reducer with isPlayerOnly.

Full screen needs to be a separate prop so that GUI knows what to show when exiting full-screen (either player-only or full editor).

- set `gui-body * {box-sizing: border-box;}` instead of expecting it to be set by the enclosing component/playground, and removed uses of content-box (adjusting sizes as needed) 
- Added `!isPlayerOnly` to the conditions for draggable sprites
- rewrote player example to use player mode.

- export image and sounds in dist/static/assets
- rename main export (`scratch-gui.js`, not `index.js`)
- move project-loader-hoc back to lib (VM doesn’t load properly without it)

Don’t translate IE error modal, if there are errors during the `connect` process the `IntlProvider` doesn’t get set up and the error modal can’t be shown.

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