Generalizes the allowedToView function to enable login-to-view with github, twitter, and oauth2.

remove code for old bug that's gone now, and enable allowed_usernames to be "*" to allow any user who can authenticate.

made it so that both argv.allowed_domains and argv.allowed_usernames can exist at the same time, and the system will still work.

slightly changed console log when there is an error processing the config parameters.

Add explanation and link to configuring the login-to-view system.

I'll keep editing this more soon, just wanted to see how it showed up on GitHub, and if it would be added to my existing PR.

adding examples

switched to authorizing users to view based on their id rather than username.

better explain how to configure config properties: allowed_domains and allowed_ids

change to more generic example of allowed_domains