[TYPO3-calendar] Dropping Date class and use DateTime and IntlDateFormatter instead of strftime() or date()

[Simon Schick]

Hi, all

I know - I really want to change stuff here ... but just throwing the 
idea :)

I would like to see the class Date replaced by DateTime and all 
date-calculation using native PHP functions like IntlDateFormatter.

By using strftime() or date() you can just get a 3-char short-version of 
the week-day. But in Germany it's quite unusual to have a 3-char 
short-version of your week-day. We're just using a 2-char short-version.
This all is supported by the class IntlDateFormatter.

Bye
Simon