Make OneToOne releations bi-directional

[belopash]

No description provided.

[eldargab]

What is the case which bothered you enough to make a PR? :)

[belopash]

@eldargab missed the comment

type Account @entity {
    id: ID!
    publicKey: ID! @index
    stashOf: Staker @derivedFrom(field: "stash")
    controllerOf: Staker @derivedFrom(field: "controller")
}

type Staker @entity {
    id: ID!
    stash: Account! @unique
    controller: Account @unique

    ...
}

need to query account in code to get controllerOf relation

[belopash]

for now I patched it locally, so it's not urgent