Test Springer Citation API more

[zuphilip]

During the creation of a seperate translator for BMC #985 we encountered a new (?) API by Springer for article citation and references. Actually, this API looks promising to be useful maybe in other Springer journal articles or even books. We should test it more and decide, if we should use it on other places as well.

Example call: http://citation-needed.services.springer.com/v2/references/10.1186/s13068-015-0395-8?format=refman&flavour=citation