Revert "Remove error serialization/deserialization (#3110)" (#3151)

This reverts commit 76ac941.

core/src/core/committed.rs

@@ -22,7 +22,7 @@ use util::secp::pedersen::Commitment;
 use util::{secp, secp_static, static_secp_instance};
 
 /// Errors from summing and verifying kernel excesses via committed trait.
-#[derive(Debug, Clone, PartialEq, Eq, Fail)]
+#[derive(Debug, Clone, PartialEq, Eq, Fail, Serialize, Deserialize)]
 pub enum Error {
 	/// Keychain related error.
 	#[fail(display = "Keychain error {}", _0)]

core/src/core/transaction.rs

@@ -210,7 +210,7 @@ impl Readable for KernelFeatures {
 }
 
 /// Errors thrown by Transaction validation
-#[derive(Clone, Eq, Debug, PartialEq)]
+#[derive(Clone, Eq, Debug, PartialEq, Serialize, Deserialize)]
 pub enum Error {
 	/// Underlying Secp256k1 error (signature validation or invalid public key
 	/// typically)

core/src/libtx/error.rs

@@ -25,7 +25,7 @@ pub struct Error {
 	inner: Context<ErrorKind>,
 }
 
-#[derive(Clone, Debug, Eq, Fail, PartialEq)]
+#[derive(Clone, Debug, Eq, Fail, PartialEq, Serialize, Deserialize)]
 /// Libwallet error types
 pub enum ErrorKind {
 	/// SECP error