[Reviewer Keith] Commonalise common operations on Route headers

There were some common memes that kept cropping up in Sprout (in fact mostly in Bono/IBCF paths) relating to handling of Route headers, so I decided to commonalise some of this into a few PJUtils methods.

I've tested it with the UT, but haven't run the live tests over it.  I watch out for live tests on staging once it is merged, but the UTs seem to cover this code quite well so I think it's unlikely anything is broken.

Mike