* Refactor usage of registry contract
* remove unsed file
* Rename methods & fix comments
* refactor contract_client:
* Intoduced separate traits for asyncronous and syncronous contract clients
* Removed registrar from ethcore::client
* s/ContractClient/AsyncContractClient
* make the tests compile and pass
* omit changes in ethcore
* Use only one trait for ContractClient
* Use an associated type in the trait to determine syncronous or asyncronous communication
* Export the types from contract-client crate
* Document that "A" in the hash correspons to a DNS A Record A.K.A Address Record
* contract_client -> registrar
* address review feedback
