add conformsTo to maDMP specification

[TomMiksa]

There should be an obligatory field in maDMPs to indicate to which version the specific maDMP conforms to, i.e. whether it conforms to release 1.0, 1.1, etc. of the specification. This information is needed for interoperability, e.g. for developers to know how to parse the file or for others to know how to interpret the terms.

For that purpose I suggest to use conformsTo in a similar way as disucssed in here ResearchObject/ro-crate#115

dmp { conformsTo : w3id.org/madmp/1.1 (...) }

Details are still to be clarified.