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

Using react-intl-redux package.

This just sets up the default English. Language switching in another PR. Requires locale/messages.json to exist, `{}` is ok.

Keep localization in the container level. Ideally we should not be passing message descriptors.

Costumes and Sound tab strings.

In order to comply to WCAG 2.0[1], buttons must have discernible text that
clearly describe the purpose, so that it can be used by screen readers.

[1] https://www.w3.org/TR/2016/NOTE-WCAG20-TECHS-20161007/H65