i18n for all templates and, json-Files for german language added

First of all, great work. NodeBB is totally awesome, I found it yesterday and played with it all day. It is great and I will totally use it!

What I did:
I overlooked all templates and replaced Strings with placeholders for i18n.
Then I added the new placeholders into the language json-files and placed the right String there.
After that I translated everything into German and put it into /public/language/de.

Hope it helps.

Greetings from Germany