This commit addresses most of the issues identified in #432:
* Support UPnP IGDs with both WANIPConnection and WANPPPConnection services
IGDs that offer both WANIPConnection and WANPPPConnection services should
now have port forwarding correctly configured for all services.
* Support multiple UPnP WANDevice and WANConnection descriptions
Per Figure 1 of the InternetGatewayDevice specification
(http://upnp.org/specs/gw/UPnP-gw-InternetGatewayDevice-v1-Device.pdf),
an IGD may have multiple WAN devices, each with multiple WANConnection
services
* Support for discovery of UPnP InternetGatewayDevice version 2 devices
* Support for discovery of multiple UPnP IGDs
Consumers that cannot yet properly process multiple IGDs can simply use
the first IGD listed in the discovery results
* Logging refinements such as friendly UPnP IGD identifiers in log messages.
