improved German translation

[rbergmair]

I'm a German native speaker, and I took a stab at improving the German translation tokens.

• added translations for some tokens that previously didn't have any translations at all
• fixed some translations that I found highly unidiomatic. (For example "Vorlieben" for "Preferences" sounds pretty weird to my ear).
• fixed some inconsistencies in spelling conventions e.g. upper-casing of personal pronouns (e.g. "Du" and "Dich" was previously upper-cased in line with conventions for writing letters in some, but not all cases. I uniformly used the lower-case version instead).

[nitely]

hey, translations are done through transifex https://app.transifex.com/spirit-project/

[rbergmair]

I've created a join request.

[nitely]

I just accepted it.

[rbergmair]

It seems like potentially a lot of work to rework this into transifex. Can you merge it here, and have transifex pick it up from here? Or is it a one-way street?

[nitely]

mmh, if you remove all the binaries, at some point I'll merge it.

[rbergmair]

That would be much appreciated, and thanks a lot for the great work you've done with this piece of software in general!

Closing in favour of #328.