Make the timezoneDetector use the locale from the parameters in the DateTimeHelper

In the DateTimeHelper, the 'locale' parameter was not used by the LocaleBasedTimezoneDetector. So the LocaleDetector was called by the LocaleBasedTimezoneDetector to guess it, even if the 'locale' was passed to the helper.

I changed it so that the LocaleDetector is not called anymore in the TimezoneDetector if a locale is passed to it.