Merge pull request #291 from tahitiangabriel/bootstrap3

Bootswatch3 : Add the Yeti Theme
Fixes #293 - Do not lower case the language
Javascript start/end date should use the date time in ISO8601 format
(yyyy-MM-ddTHH:mm:ss.SSSZZ).
Otherwise we got unpredictable result with custom format (set by
withFormat).