Handle case where user is logged into one tab and attempts to log in to another

[lognaturel]

Currently a user sees Incorrect email address and/or password. even if their credentials are correct. This is because the request includes the session cookie but not the CSRF token.

@matthew-white has suggested sending a second request to /sessions/restore and in case of a different user attempting to log in, display a message like “You are already logged in as X. Please refresh the page to continue.”