Introduce PackageTemplate, a replacement of InputMaterial

PackageTemplate aims to replace InputMaterial, introducing a clean
interface to manipulate a wide range of claim types without
OnchainTxHandler aware of special content of each.

This is used in next commits.

Author: Antoine Riard

lightning/src/ln/channelmonitor.rs

@@ -12,7 +12,7 @@
 //! ChannelMonitors to get out of the HSM and onto monitoring devices.
 
 use bitcoin::blockdata::block::BlockHeader;
-use bitcoin::blockdata::transaction::{TxOut,Transaction};
+use bitcoin::blockdata::transaction::{TxOut, Transaction};
 use bitcoin::blockdata::transaction::OutPoint as BitcoinOutPoint;
 use bitcoin::blockdata::script::{Script, Builder};
 use bitcoin::blockdata::opcodes;
@@ -459,7 +459,7 @@ pub(crate) enum InputMaterial {
 	}
 }
 
-impl Writeable for InputMaterial  {
+impl Writeable for InputMaterial {
 	fn write<W: Writer>(&self, writer: &mut W) -> Result<(), ::std::io::Error> {
 		match self {
 			&InputMaterial::Revoked { ref per_commitment_point, ref remote_delayed_payment_base_key, ref remote_htlc_base_key, ref per_commitment_key, ref input_descriptor, ref amount, ref htlc, ref on_remote_tx_csv} => {