Add community and peer address of SNMP TRAP PDUs to camel-snmp header

A patch is included to add the community and peer address of SNMP traps that are received by camel. This is useful to determine where a trap originated from, as not all SNMPv2 traps include an OID that identifies the sender.

The information is placed in the message header as strings with names:
securityName
peerAddress

These names correspond to the accessor names in the snmp4j API for the CommandResponderEvent class. securityName is not the correct name for SNMP v1/2 traps, but it's probably better to stick with a name that can be consistant between SNMP versions.