Start improving the api traits

:100644 100644 898aadc7 49217199 M	Cargo.lock
:100644 100644 61570436 465ed664 M	core/client/src/backend.rs
:100644 100644 5d0c886b 64d710fd M	core/client/src/block_builder.rs
:100644 100644 c447855e 5ecbe474 M	core/client/src/client.rs
:100644 100644 139cef13 f90dbf3d M	core/client/src/error.rs
:100644 100644 2800c503 3298e66a M	core/client/src/runtime_api.rs
:100644 100644 affa1c5c 809b08bc M	core/primitives/src/lib.rs
:100644 100644 2877dfa9 d5547413 M	core/sr-api/Cargo.toml
:100644 100644 9a49784d 6a625a03 M	core/sr-api/src/lib.rs
:100644 100644 7c28e1c7 a1a444a9 M	core/sr-primitives/src/traits.rs
:100644 100644 2e113ab6 dcc01a6d M	srml/metadata/Cargo.toml
:100644 100644 ea722a70 0809531a M	srml/metadata/src/lib.rs