We were escaping the URL before performing any pattern matching on it.
This meant that if you sent data that URLdecoded to a "/", it would count as
a "/" in the URL, potentially causing a 404. This was causing some flaky tests
with some randomly-generated query parameters.
Now, we keep URLs encoded while doing the pattern matching, and only afterwards
do we URL decode each query parameter individually before passing them to their
respective handler functions.
github.com/gorilla/mux was also updated to v1.7.3 to fix a bug with URL encoding and subrouters.
Fix Docker files which had been forgotten in #594 and update scripts and docs to remove references to gb.
I also removed the `jenkins` directory which is outdated. We can revert f8d7e99 if we realise that it was a mistake to do so.
