Add german as context, #510

[Phu2]

Pages created from markdown should be in the german context for now as there are only german versions available.

[sroertgen]

LGTM

@Phu2: only thing I noticed is that on some pages there is "Gewährleistung" in the footer, e.g. when being on the "usage policy" page. on others there is not

If you can clarify if this is expected, I will merge

[Phu2]

@sroertgen Well, unfortunately my changes were overwritten on http://stage.lobid.org/usage-policy/, but you can still see them on http://test.lobid.org/usage-policy/