* Move module metadata from json string to custom metadata
* Revisit the metadata structures
1. Move the structures into the metadata crate.
2. Switch to using Cow/MaybeOwnedArray to support Encode/Decode
* Adapt to new metadata structures
* Convert event json metadata to new metadata structures
* Convert storage json metadata to new metadata structures
* Convert runtime metadata from json to new metadata structs
* Implements new metadata structures in client and runtime
* Fixes errors on `no_std`
* Fixes errors after rebasing master
* Do not use `Cow` anymore in metadata
Also replace `String` with our own type definition `StringBuf`.
This fixes compilation on `no_std`.
* Wrap `RuntimeMetadata` in `RuntimeMetadataVersioned` to support versioning
* Move metadata into `srml` and make core unaware of the implementation
guanqun