Corrections and additions for the German language pack.

[wehro]

This includes additions for semicolon related messages and stylistical improvements.

[sangwinc]

Thanks @wehro for your continued interest. This is very helpful.

It's really important that language strings go through the Moodle translation process: https://lang.moodle.org/

Currently, only German language is distributed with STACK itself, because of the API. And @EJMFarrow just committed changed to dynamically download language packs as needed within the API, so this won't be necessary in the future. Indeed, if not we'll delete the German language file to avoid this kind of confusion!

You'll notice that I changed your pull request into "dev", because we just updated the German language pack here.

I submitted some of your suggestions through the Moodle translation process already, for review by the Moodle language pack maintainer.