* Unify error enums in substrate and ethereum clients with `thiserror`

Related to https://github.com/paritytech/parity-bridges-common/issues/857

* Add license pre-amble

* rustfmt

* Fix spelling

* shared conversion rate metric value

* clippy

* administrative metrics

* fmt

* fix compilation

* fix compilation again

* and another one

* remove GenericLoopMetrics

* chttp -> isahc

* remove redundant marker

* not about price metrics

* fmt

* Remove chains.

* Move relay clients.

* Flatten generic.

* Fix fmt.

* Nest some crates.

* Alter command execution to make it easier to add new bridges.

* Rename sub-dirs.

* cargo fmt --all

* Address clippy.

* Update relays/substrate/src/rialto_millau/cli.rs

Co-authored-by: Hernando Castano <[email protected]>

Co-authored-by: Hernando Castano <[email protected]>

* Make Substrate deps uniform

* Rest of the deps.

* Fix broken merge.

* Revert substrate.

* Fix tests

Co-authored-by: Pierre Krieger <[email protected]>

* extract common parts of relay loops: begin

* merge client impls

* backoff in exchange loop

* reconnect without clone

* reward confirmation relayer

* Update modules/message-lane/src/instant_payments.rs

Co-authored-by: Hernando Castano <[email protected]>

* added some constants

* pallet_balances

* removed comment

* fix typo

Co-authored-by: Hernando Castano <[email protected]>

* migrate back to Substrate master

* fmt

* clippy

* get Substrate dependencies from crates.io

* removing unused dependencies

* cargo fmt --all

* remove commented dependencies

* remove commented dependencies again

* try to fix compilation

* Change script to update versions.

* Bump versions.

* Address remainders.

* cargo fmt --all

* Fix tests.

* Whitelist BlueOak license

* Fix benchmarks?

* extracted relay crates

* moved metrics to utils

* exchange-relay compilation

* fix compilation of headers-relay

* fixed messages-relay compilation

* fixed ethereum-poa-relay compilation

* cargo lock

* cargo fmt --all

* clippy

* cargo fmt --all

* fix tests compilation

* clippy

* eof

* module level docs

* removed obsolete comment

* #![warn(missing_docs)]

* .0 -> Deref

* post-merge fix

* cargo fmt

* Update relays/headers-relay/src/headers.rs

Co-authored-by: Hernando Castano <[email protected]>

* Update relays/headers-relay/src/headers.rs

Co-authored-by: Hernando Castano <[email protected]>

* Update relays/headers-relay/src/lib.rs

Co-authored-by: Hernando Castano <[email protected]>

Co-authored-by: Hernando Castano <[email protected]>