Request for adding proper support for localization/internationalization

[tgurr]

Right now it seems to be quite cumbersome to try to translate the frontend. Some strings are scattered across various index.js and index.jsx files and others I wasn't even able to find e.g. the strings for the search/. It would be great if we could have a central file for every localization, something like: https://github.com/vector-im/riot-web/tree/develop/src/i18n/strings