Adds the following API functions:
- API to get signature key IDs for mobile:
func (msg *PGPMessage) GetHexSignatureKeyIDsJson() []byte
- API to get encryption key IDs for mobile:
func (msg *PGPMessage) GetHexEncryptionKeyIDsJson() []byte
- API to get the number of key packets in a PGP message:
func (msg *PGPSplitMessage) GetNumberOfKeyPackets() (int, error)
- API in package `helper` to encrypt a PGP message to an additional key:
func EncryptPGPMessageToAdditionalKey(messageToModify *crypto.PGPSplitMessage, keyRing *crypto.KeyRing, additionalKey *crypto.KeyRing) error
