Discourse modifications for federated sign-in compatability with ECHOcommunity

What it does:

• Modifies SSO to send login requests to a remote host with a return path
• Reads ECHOcommunity shared session cookie and performs user authentication from redis

Changelog:

1.8.0 - 2.3.0 FIX: Match numbrer of arguments for impersonation method for Discourse v2

1.8.1 - 1.8.2 Now allows for impersonation. Use "logout" to end impersonation and return to administrator session.