Change log in text

[BronsonQuick]

As per Paul's comment we should change the wording from "Login with Delegated Auth" to something more user friendly such as "Log in with your HM Central account"

[rmccue]

Let's make sure this is configurable, as this plugin isn't just for HM Central. Looks like we're using constants for the URL config, so could use the same for the text; I wonder if both should be moved to options instead though.