Reworked and extended German localization.

The prevalent German localization is incomplete (missing more recent features like time zone and FAQ) and suffers from translations, orthographic and grammatic errors. In addition, there is no clear concept of addressing the user (German has a polite and an informal way of addressing other people). As a result, the web page appears rough and incomplete to the German user's eye. This patch should bring the web page to a level where it is feature complete and mostly free of errors and inconsistencies.