Add changes to support German / Austria events / locale

[the42]

Not tested using Lektor

[smth]

I've put this live, with a couple of changes:

• Removed last paragraph of the "About" section. There wasn't enough space, and the local event details should be added to the map (once we have a map). https://github.com/okfn/opendataday/commit/cd7bee5639b0ed2db8494b3f04e6f5e82064a849
• Added language: de_at to the content file. This is needed for the language selector. https://github.com/okfn/opendataday/commit/c5599d2f63ba924612584795c584e3bfe61093bc