Offirmo's internationalize

Based on yahoo i18n libs (http://formatjs.io/), but offering more:

• integrated Intl API polyfill (taken from yahoo doc itself)
• simpler API (keeping all features,
• safer failover

While message resolution may fail, we try to not aggressively fail with a throw, but instead return the "best possible message":

• never throw, always return a displayable string
• fallback to "en" if possible
• display a raw key to the user (in UI) rather than nothing, to ease pinpointing
• allow passing a custom debug id to more easily identify components with broken i18n

TODO add a customizable error handler

Interesting reads:

• http://userguide.icu-project.org/formatparse
• http://userguide.icu-project.org/formatparse/messages
• http://formatjs.io/