Reviewer MIRW: Mangelwurzel

Hi Matt,

Please can you review my mangelwurzel code?

This pull request includes full UT coverage.

I've also done some fairly basic live testing, but in particular I've got mangelwurzel in a call working as a B2BUA and mangling the dialog identifiers, Req URI, Contact URI, To URI, Route-sets and stripping and re-adding Via headers. I haven't done any (successful end to end call) testing with the change_domain flag set since I think there is very little risk of this not working (given the testing I have done and my UTs) and it'll be a pain to configure.

(Incidentally, the testing I have done was pretty easy to setup - use chef to spin up a mangelwurzel, configure mangelwurzel in ellis and make a call).

Let me know if you have any questions!

Thanks,
Graeme