Add frontend SSO endpoints, expand troubleshooting support

Updates included:

* New SSO controller and settings for frontend sign on.
* New log viewing interface for viewing the `zendesk.log` file. Also allow easy downloads and clearing of this file.
* Expand the logging used in the API to help troubleshoot problems.
* Add connection testing buttons to the configuration page, to help diagnose networking (web server, firewall, etc) problems when attempting to access the API.