add de translation

[emdete]

this is a "blind" translation of the english string to german without check/test in the real app. maybe some polish is needed for one or two phrases to be accurate in the gui (but i have to read the source for that).

[jmatsushita]

Many thanks for the translation. It has been merged into our Alpha branch. You can request an alpha tester account to check/test in the real app:

• Joining this Google+ community https://plus.google.com/communities/101207607341438433206
• Click on "Become a tester" on this page: https://play.google.com/apps/testing/org.iilab.pb

Regarding workflow, I realise now that I should have mentioned that the json files (not the values-de files) are actually generated from a jekyll instance so that they can be edited using Prose. I have added you to the relevant repository and you can access the admin interface through this link : https://admin.panicbutton.io/#iilab/teampanicbutton.github.io

Pushing to this repo (or saving within prose) will automatically publish this file : https://panicbutton.io/api/de/mobile.json which can then be saved into the /assets folder (It used to be automatically updated but we changed this for security reasons #40).

Also note that it was suggested (#43) that we make the project compatible with transifex.