Reworked and extended German localization.

The prevalent German localization is incomplete (missing more recent features like time zone and FAQ) and suffers from 1:1 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.