Fix relative urls in Cards

[HLWeil]

@Freymaurer, not deep into webdev so not sure if this is a proper solution.

But using this on my branch for now for ease of use and putting up this PR as a reference

[HLWeil]

Okay fixed now, created URL aliases for the already exisitng markdown files. Renamed "Annotation Principle" to "Research Data Principle", as proposed by @muehlhaus

[Freymaurer]

Awesome!