Cleanup in pre-defined AuthProviders.

[ghost]

1. All pre-defined AuthProviders contain unused code in form of this computed property:

	private var appAccessToken: String {
		return clientID + "%7C" + clientSecret
	}

This property is never accessed by the other code.

2. The comment style is quite inconsistent. There are /// comments and /** **/ comments.
   Notably, there are comments that seem to have been straightly copied from the Turnstile repository, e.g.

	/**
	Create a Facebook object. Uses the Client ID and Client Secret from the
	Facebook Developers Console.
	*/

In this case, the leading indentation got misaligned while copying. The original seems to be here:
https://github.com/stormpath/Turnstile/blob/master/Sources/TurnstileWeb/LoginProviders/Facebook.swift

3. There are indicators that suggest that the various AuthProviders seem to have been copy pasted between each other. For example, there is a fb variable in non-Facebook auth providers.

4. There is lots of commented-out code, empty lines and in case of SalesForce personal user information containing names, user IDs and coarse location information. While this is not a strictly technical problem, it does not provide the impression that this code is ready for production, especially as this code is the first thing one has to look at when integrating a custom AuthProvider.