cli: allow to send multisig deploy/invoke tx

It allows to invoke native contracts as committee
from CLI in privnet, e.g. to set new oracle nodes.

Also don't require `out` flag in `multisig sign`
if tx is to be pushed.

cli/paramcontext/context.go

@@ -0,0 +1,53 @@
+package paramcontext
+
+import (
+	"encoding/json"
+	"fmt"
+	"io/ioutil"
+
+	"github.com/nspcc-dev/neo-go/pkg/core/transaction"
+	"github.com/nspcc-dev/neo-go/pkg/smartcontract/context"
+	"github.com/nspcc-dev/neo-go/pkg/wallet"
+)
+
+// validUntilBlockIncrement is the number of extra blocks to add to an exported transaction
+const validUntilBlockIncrement = 50
+
+// InitAndSave creates incompletely signed transaction which can used
+// as input to `multisig sign`.
+func InitAndSave(tx *transaction.Transaction, acc *wallet.Account, filename string) error {
+	// avoid fast transaction expiration
+	tx.ValidUntilBlock += validUntilBlockIncrement
+	priv := acc.PrivateKey()
+	pub := priv.PublicKey()
+	sign := priv.Sign(tx.GetSignedPart())
+	scCtx := context.NewParameterContext("Neo.Core.ContractTransaction", tx)
+	if err := scCtx.AddSignature(acc.Contract, pub, sign); err != nil {
+		return fmt.Errorf("can't add signature: %w", err)
+	}
+	return Save(scCtx, filename)
+}
+
+// Read reads parameter context from file.
+func Read(filename string) (*context.ParameterContext, error) {
+	data, err := ioutil.ReadFile(filename)
+	if err != nil {
+		return nil, fmt.Errorf("can't read input file: %w", err)
+	}
+
+	c := new(context.ParameterContext)
+	if err := json.Unmarshal(data, c); err != nil {
+		return nil, fmt.Errorf("can't parse transaction: %w", err)
+	}
+	return c, nil
+}
+
+// Save writes parameter context to file.
+func Save(c *context.ParameterContext, filename string) error {
+	if data, err := json.Marshal(c); err != nil {
+		return fmt.Errorf("can't marshal transaction: %w", err)
+	} else if err := ioutil.WriteFile(filename, data, 0644); err != nil {
+		return fmt.Errorf("can't write transaction to file: %w", err)
+	}
+	return nil
+}