Move default messages into Globalize

As discussed in https://github.com/rxaviers/react-globalize-compiler/pull/5, the fact that react-globalize monkeypatches Globalize to support default messages (ie. using the string in the default language as the key for the message) complicates the code for react-globalize-complier and globalize-compiler. Large projects that use both react-globalize elements and calls to Globalize.`messageFormatter`/`formatMessage` can run into complications - some code might hit a Globalize that has been monkeypatched, while other code might hit an unpatched Globalize object.

If the default messages code were moved into Globalize itself, this would be much simpler.