Testing of proxy-prefix setting

@shiltemann noticed a possible issue in one of the routes due to their proxy-prefix settings. I've had similar issues in the past that I only caught because I used a proxy-prefix (and `remote_user`.) Would it be possible that we add an additional run of the selenium tests (or one of the web-based ones) with the prefix set to something like `/galaxy`? This would save deployers some time during upgrades. @jmchilton how hard would this be to do?

Start by locating the Selenium tests and other web-based test entry points, then inspect how proxy-prefix and remote_user are configured for test runs. Add coverage for a prefix such as /galaxy and verify that the relevant routes work under it. Done means the prefixed test run executes successfully and catches route regressions.

Written by the indexing model from the issue text.