Add "rotateDidFrom" and "rotateDidTo" to support DID Rotation

[peacekeeper]

This PR is an attempt to define DID document update operations that implement the concepts in DID Rotation, using the generic DID Registration interfaces.

[peacekeeper]

@fabianekc

[fabianekc]

some thoughts on documenting DID Rotation:

section: didDocumentOperation="rotateDidFrom"

• add info, that the DID document content is maintained
• add statement, to create a new DID first with the exact content of the original DID
• add requirement to only perform operation when new DID has same content as original DID

section: didDocumentOperation="rotateDidTo"

• add info, that the DID document content is maintained
• add requirement to verify before rotateDidTo-operation that alias to new DID exists in original DID
• add requirement to verify before rotateDidTo-operation that original DID must be deactivated

other aspects:

• what happens if only rotateDidFrom operation is performed
  • => Resolver must not resolve to new DID because back-reference is missing and history would be broken
• what happens during the timespan between performing rotateDidFrom and rotateDidTo
  • => Resolver would report deactivated DID but could hint that a Rotation process is ongoing
• what happens if only rotateDidTo operation is performed
  • => Resolver must not access original DID Document and previous versions of the original DID Document