Updated the logout link in the UI to use a link provided by the
/chronograf/v1/ endpoint. We also replaced many instances of string
concatenation of URL paths with path.Join, which better handles cases
where prefixed and suffixed "/" characters may be present in provided
basepaths. We also refactored how Basepath was being prefixed when using
Auth. Documentation was also updated to warn users that basepaths should
be applied to the OAuth callback link when configuring OAuth with their
provider.
Tim Raymond & Jared Scheib
Chris Goller