Allow :format option lookup via I18n or DATE_FORMATS hashes

First attempts to find the passed in :format option in:
- I18n time.formats.{format}
- I18n date.formats.{format}
- Time::DATE_FORMATS
- Date::DATE_FORMATS
Else, returns the passed in :format option straight up or, if blank, uses the
default format: '%B %e, %Y %l:%M%P'.