[improvement] Make Store trait for all layer data stores

[Andyou007]

subject

Now I and C-Engine is deserved to define and require store implement. StoreClient will be corrccted to Store, client to store, _load to _get, _store to _set.

[Andyou007]

signature is here:

`
trait Store {
type Identity;
type Index;
type Schema;
type Data;
type Parameter;
type Error;

fn get(
    &mut self,
    identity: &Self::Identity,
    index: &Self::Index,
    schema: &Self::Schema,
    data: &Self::Data,
    parameter: &Self::Parameter,
) -> Result<&[usize], Self::Error>;

}
`