Added missing items, fixed spelling errors and smoothed some wording

First time contributing to someone else's code, so please excuse and point out any violation of (un)written rukes. But I love kanboard and couldn't stop myself...

Most of it is spelling, and what I believe convention ("" vs. «» - technically German uses one down one up, but don't know if that works here). The rest is trying to make it sound more German, which obviously is very subjective.