service: define and implement Token field composing interface

This commit:

  * defines SessionToken interface of Token field getters/setters group;

  * implements SessionToken on Token message.

refs/types.go

@@ -37,6 +37,18 @@ type (
 	OwnerID chain.WalletAddress
 )
 
+// OwnerIDContainer is an interface of the container of an OwnerID value.
+type OwnerIDContainer interface {
+	GetOwnerID() OwnerID
+	SetOwnerID(OwnerID)
+}
+
+// AddressContainer is an interface of the container of object address value.
+type AddressContainer interface {
+	GetAddress() Address
+	SetAddress(Address)
+}
+
 const (
 	// UUIDSize contains size of UUID.
 	UUIDSize = 16