Return appropriate error message on import wallet

Fix https://github.com/TrustWallet/trust-wallet-ios/issues/31

Trust/EtherClient/EtherKeystore.swift

@@ -54,7 +54,7 @@ class EtherKeystore: Keystore {
             let _ = setPassword(password, for: account)
             return (.success(account))
         } catch {
-            return (.failure(.failedToImport))
+            return (.failure(.failedToImport(error)))
         }
     }
 

Trust/EtherClient/KeyStoreError.swift

@@ -5,7 +5,7 @@ import Foundation
 enum KeyStoreError: LocalizedError {
     case failedToDeleteAccount
     case failedToDecryptKey
-    case failedToImport
+    case failedToImport(Error)
     case failedToSignTransaction
 
     var errorDescription: String? {
@@ -14,8 +14,8 @@ enum KeyStoreError: LocalizedError {
             return "Failed to delete account"
         case .failedToDecryptKey:
             return "Could not decrypt key with given passphrase"
-        case .failedToImport:
-            return "Failed to import keystore"
+        case .failedToImport(let error):
+            return error.localizedDescription
         case .failedToSignTransaction:
             return "Failed to sign transaction"
         }

Trust/Extensions/Error.swift

@@ -31,4 +31,7 @@ extension Error {
             return "Undefined Error"
         }
     }
+
+    var code: Int { return (self as NSError).code }
+    var domain: String { return (self as NSError).domain }
 }