Annotations: Take content identifier into account

[stefandesu]

jskos-server now automatically adds a mapping's content identifier to an annotation if possible: gbv/jskos-server#173

This means we can now compare this identifier (annotation.target.state.id) to the mapping's current content identifier to see if the mapping has changed, and if it did, these annotations should not be taken into account. (They can still be shown as "invalid" with a hint that the mapping has changed in the meantime.)

If possible, the creator of such an annotation should be able to update that annotation. This should perform a PATCH request that updates the identifier in target.state.id. We need to figure out a good UI to do this.

Should be taken into consideration for #682.

Related to #667.

[stefandesu]

these annotations should not be taken into account

Update: This is probably too complicated. An easier solution would be to allow a mapping creator to delete these invalid annotations after they updated the mappings. This needs to be implemented in jskos-server. (Issue TBD.)