Make `Get` method of the wrapper over Container contract's client to
accept binary container ID. Create `Get` function similar to the previous
`Get` variation. Use this function in Container service server in the place
where `Get` method was used.
Additionally implement `AsContainerSource` function which allows
to simply compose container Source interface from the wrapper.
Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>
83c27f6e8a