OpenID Login process: Visually indicate login flow

When a login form is displayed to a user while in an OpenID login flow, this should be visually distinguishable. Currently, it looks like the user had randomly dropped out of wherever they were trying to login, and moved to AlekSIS for some inobvious reason.

We could remove AlekSIS decorations for the login view (and the OAuth grant view) if login happens during an OpenID login process, and add a textual note about what is happening.