As I gadget developer I want to get data of a statement of an item or property, so I can use it my gadget.
As I gadget developer I want to create a statement on an item or property, so my gadget can be used to store new statement.
As I gadget developer I want to modify a statement on an item or property, so my gadget can store changes made by its user.
As I gadget developer I want to delete a statement from an item or property, so my gadget can store changes (deletions) made by its user.
**Notes**
* See proposal of GET/PUT/PATCH/DELETE /statements/{statement_id}, and POST /entities/items/{item_id}/statements in 2020 schema propsal: https://wmde.github.io/wikibase-rest-api-proposal/#/statements
* When creating the stories, be sure to cover both getting a single and a list of statements
* @Silvan_WMDE to quote the RFC that highlights that body of DELETE requests might be skipped by servers (which might lead to us changing the schema for DELETE requests, compared to the 2020 proposal)