IChannel interface created to abstract away the inner MessageProcessor in clients.

WcfChannelFactoryWrapper renamed to WcfChannel. It is implementing IChannel.
WcfClient now uses an IChannel inner processor.
BuildAgentClientBase does not implement IMessageProcessor anymore - message handling is implementation detail of the WcfClient.
EchoMessage method added to BuildAgentClientBase.
WcfClient's SendMessage returns a failed response when trying to send messages to a disconnected buildagent.
Basic project and task interfaces added.

IntegrationRequest and IntegrationResponse messages added.