XEP-0297 Stanza Forwarding and XEP-0280 Message Carbons

XEP-0297: Stanza Forwarding implementation

This patch adds Forwarded.java, a class to wrap messages forwarded
from a different entity. A forwarded stanza contains of a Packet and
an optional timestamp.

WARNING: The current implementation only allows to forward Message
packets, as there is no universal way to parse a Packet from SMACK.

XEP-0280 Message Carbons implementation

This patch adds Carbon.java, a class to wrap the packet extension
defined in XEP-0280 to store copies of messages sent to or received
by a user to his other client(s).

The CarbonManager allows to register XEP-0280 support with the SDM,
to enable and disable the feature and to manipulate messages
accordingly.

Signed-Off-By: Georg Lukas <georg@op-co.de>
Merge pull request #16 from ge0rg/xep0280

XEP-0280 and XEP-0297