Settings accepting URLs should be ambivalent about tailing slashes

[HitScan]

When entering a URL such as the baseURL or Overdrive Patron API url, users may or may not include a tailing '/' at the end of the value. Aspen should be able to make use of the value whether such a slash is or isn't present, but currently a trailing slash at the end of the OD patron api url at least will cause failures to contact the service.