Add German translation for chat/clients/adium

It should be checked whether the menu items/tabs in Adium are called the way I addressed them in this translation. I don't own a Mac and cannot check them myself.
Use https://adium.im instead of the unencrypted url
Merge pull request #159 from rosetree/master

Add German translation (adium)
Merge remote-tracking branch 'upstream/master'