Allow multiple roles for contributors

[peterdesmet]

Contributors currently need to be repeated if they have multiple roles. That is because role is a string rather than array value in Frictionless. I have submitted this as a request for change at frictionlessdata/datapackage#804

Should Camtrap DP already go ahead a allow multiple values for role?

• Advantage: more concise representation
• Disadvantage: will break Frictionless validation, unless we mint our a new term like roles

[peterdesmet]

Discussed with @kbubnicki, moved to 1.1. That means that Camtrap DP 1.0 will require to repeat contributors when they have multiple roles. That is somewhat annoying, but it also doesn't break validation and doesn't make it complex to allow it later (when e.g. frictionlessdata/datapackage#846 is accepted).