Small QoL improvements for wallet developers (#2651)

* Small changes for wallet devs

* Move create_nonce into Keychain trait

* Replace match by map_err

* Add flag to Slate to skip fee check

* Fix secp dependency

* Remove check_fee flag in Slate

wallet/src/types.rs

@@ -131,6 +131,10 @@ impl WalletSeed {
 		Ok(WalletSeed::from_bytes(&bytes))
 	}
 
+	pub fn to_bytes(&self) -> Vec<u8> {
+		self.0.clone()
+	}
+
 	pub fn to_hex(&self) -> String {
 		util::to_hex(self.0.to_vec())
 	}