Move ethcore::Error to error_chain (#8386)

* WIP

* Convert Ethcore error to use error_chain

* Use error_chain for ImportError and BlockImportError

* Fix error pattern matches for error_chain in miner

* Implement explicit From for AccountsError

* Fix pattern matches for ErrorKinds

* Handle ethcore error_chain in light client

* Explicitly define Result type to avoid shadowing

* Fix remaining Error pattern matches

* Fix tab space formatting

* Helps if the tests compile

* Fix error chain matching after merge

ethkey/src/error.rs

@@ -14,7 +14,7 @@
 // You should have received a copy of the GNU General Public License
 // along with Parity.  If not, see <http://www.gnu.org/licenses/>.
 
-use std::fmt;
+use std::{fmt, error};
 
 #[derive(Debug)]
 /// Crypto error
@@ -51,6 +51,12 @@ impl fmt::Display for Error {
 	}
 }
 
+impl error::Error for Error {
+	fn description(&self) -> &str {
+		"Crypto error"
+	}
+}
+
 impl Into<String> for Error {
 	fn into(self) -> String {
 		format!("{}", self)