multi: use witnessScript everywhere instead of redeemScript

This commit consists of a mass variable renaming to call the pkScript being executed for segwit outputs the `witnessScript` instead of `redeemScript`. The latter naming convention is generally considered to be reserved for the context of BIP 16 execution. With segwit to be deployed soon, we should be using the correct terminology uniformly through the codebase. 

In addition some minor typos throughout the codebase has been fixed.

lnwallet/interface.go

@@ -210,19 +210,19 @@ type BlockChainIO interface {
 	GetTransaction(txid *wire.ShaHash) (*wire.MsgTx, error)
 }
 
-// SignDescriptor houses the necessary information required to succesfully sign
+// SignDescriptor houses the necessary information required to successfully sign
 // a given output. This struct is used by the Signer interface in order to gain
-// access to critial data needed to generate a valid signature.
+// access to critical data needed to generate a valid signature.
 type SignDescriptor struct {
 	// Pubkey is the public key to which the signature should be generated
 	// over. The Signer should then generate a signature with the private
 	// key corresponding to this public key.
 	PubKey *btcec.PublicKey
 
-	// RedeemScript is the full script required to properly redeem the
+	// WitnessScript is the full script required to properly redeem the
 	// output. This field will only be populated if a p2wsh or a p2sh
 	// output is being signed.
-	RedeemScript []byte
+	WitnessScript []byte
 
 	// Output is the target output which should be signed. The PkScript and
 	// Value fields within the output should be properly populated,