ensure endpoint paths are retained when setting the version prefix

fixes #34

ActiveResource ignores site.path when a prefix is set. Since we're
always using setting versions as the prefix, we always include the site.path.

Test API configuration no longer has a password so we don't have to set
self.password = nil all over the tests. This created a side-condidtion
where connections with overridden endpoint configuration were saved on
Daylight::API subclasses.

Updated Daylight::Mock to not fail when a user or password wasn't
configured.