[Reviewer: Ellie] Unescape URLs before creating SAS log in HttpConnection, for consistency...

... with HttpStack

Fixes one of the issues in https://github.com/Metaswitch/sprout/issues/538. UTed in https://github.com/Metaswitch/sprout/pull/693.

UTed but not live-tested - I'm going to make a bunch of SAS fixes, live-test them together for efficiency, then merge.