Merge branch 'develop' into greenkeeper/scratch-l10n-3.0.20180712200642

package.json

src/components/connection-modal/connection-modal.css

src/components/connection-modal/connection-modal.jsx

src/components/connection-modal/icons/scratch-link.png

src/components/connection-modal/unavailable-step.jsx

src/containers/connection-modal.jsx

src/containers/costume-library.jsx

src/containers/costume-tab.jsx

src/containers/stage.jsx

src/lib/file-uploader.js

src/lib/libraries/backdrops.json

src/lib/libraries/costumes.json

src/lib/libraries/extensions/index.jsx

src/lib/libraries/sprites.json