access.ajxp_user: Translate some german strings

Where I'm quite certain they're correct.
access.ajxp_home: Getting started translated to german

This was forward-ported from a patch we had against 5.3.1 and
mostly completed the "getting started" section translation.

Sponsored-by: Gymnasium Köniz-Lerbermatt
Merge pull request #603 from matsimon/german-i18n-userfacing

i18n: Add some more user-facing german strings