Added create on failing translate and updated TranslateMe construction

- Changed method of defining the getLocale function when constructing
TranslateMe. You now have to override the getLocale function from the
TranslateMe object, if you want an custom behaviour.
- Changed the default behaviour of getLocale to return the best
language based on the reuests header "accpeted-languages"
- TranslateMe now registers the locale middleware by itself
- Enhanced "/i18n/translations" (post) to check for required parameters
and respond accordingly. Furthermore enabled creation of new
translation without a locale. In this case the default locale will be
used.
- Added support for requesting translations based on multiple locales
in "/i18n/translations" (get). Furthermore you can now retrieve all
translations, by passing no locale parameter.
- Enhanced stripping of "ns:" placeholder in underscore.translate