EpochSolution Inspection RuntimeApi and RPC Method

[mustermeiszer]

The api should provide the possibilities to call a node whether a solution is valid for given pool and how the respective score of this solution would be.

Implementation Proposal

#[rpc]
pub trait EpochSolutionApi {
	#[rpc(name = "pools_inspectSolution")]
	fn inspect_epoch_solution(&self, id: T::PoolId, solution: Vec<TrancheSolution>) -> Result<EpochSolution<Balance>>;
}

decl_runtime_apis! {
    pub trait EpochSolutionApi {
	 fn inspect_epoch_solution(id: Hash) -> Option<EpochSolution<Balance>>;
    }
}