Don't change the identifier in the item saved to the store

[j-mai]

Currently, when generating a key for a push request, the identifier that the client provides is overridden by the hashed key in this line:

argus/store/transport.go

Line 88 in 8a73715

item.Identifier = transformPushItemID(item.Identifier)

The user provided identifier should be saved as part of the resource. the push request object should probably include a Model.key as part of the struct instead. This way, when the user grabs all the resources or that specific resource, they can see the identifier they provided.