Add support for Energy Web Foundation's new chains (#10957)

* add(chain-support): new ewf chains support added

- volta test network
- ewc production chain

* remove(tobalaba): ewf chain tobalaba support removal

- tobalaba is deprecated so not officially supported by ewf any more

ethcore/src/spec/chain.rs

@@ -76,7 +76,8 @@ bundle_release_spec! {
 	"ethereum/poasokol" => new_sokol,
 	"ethereum/rinkeby" => new_rinkeby,
 	"ethereum/ropsten" => new_ropsten,
-	"ethereum/tobalaba" => new_tobalaba
+	"ethereum/volta" => new_volta,
+	"ethereum/ewc" => new_ewc
 }
 
 bundle_test_spec! {