[Reviewer: Graeme] Craft logging Enhanced Node Troubleshooting 

Added PDLog infrastructure (definition in new header, craft_dcea.h) and PDLogs for http and sip.
We could use -Wno-format-nonliteral, which I think would turn off this specific warning but leave the more useful one where the format string is a literal but doesn't match the parameters.  Don't mind too much either way - and happy with the rationale for using templating.