[types]: ID type instead of serde_json::RawValue (#325)

* get started

* add additional test

* fix nits

* cargo fmt

* [types]: write some tests.

* [http server]: send empty response on notifs

* [http server]: fix tests

* [rpc module]: send subscription response

* Update types/src/v2/error.rs

* fix nits

* cargo fmt

* Update types/src/v2/params.rs

* remove needless clone

* remove dead code

* [types]: impl PartialEq for JsonErrorObject + test

* use beef::Cow

* Update http-server/src/tests.rs