Sanitize login-screen -flow

[olmari]

EDIT: On the deeper thought, generally login-screen (be it just another page or modal or anything) should offer exactly only login related stuff, if there is need for help-menu or something alike, it should then open to new window/tab. While even more important on SSO-login -flow, it is not restricted to SSO.

Original: At the moment SSO-login flow shows basically exact same screen that normal mulysa login would. We'd need to not show "Become an member" nor the sitename to link to "front page" etc... Generally we'd need to show only the login option and no way to surf outside of login scope.