Add basic logging interface

Will show the contents of the Zendesk log file. If the file is too large
then only the last 1000 lines will be shown, to avoid problems with the
page taking too long to render.

There is also a button available to directly download the entire file.
Add new SSO functionality for end-user and agents

Requires the updated Zendesk interface which separates the frontend and
backend, so that SSO requests can go through to the right area of
Magento.

Also adds some additional debugging functionality.
Add connection checks for APIs

Performs a basic check on the Zendesk API and the custom Magento API, to
allow admins to easily determine if they are working as expected.

As the Magento API needs to be tested from an external location, an AJAX
request is sent from the browser to determine if the API is accessible.
Version bump
Add log clearing and SSO logout
Add logout method for admin SSO
Add translations for new strings
Fix whitespace issues, add en_US translation
Change magic number for max log size to constant
Add troubleshooting link to test responses
Merge pull request #14 from fontis/add_sso_logging

Add frontend SSO endpoints, expand troubleshooting support