restore mediawiki username escape for backward-compat
restore mediawiki username escape for backward-compat

santi81/oauthenticator,maltevogl/oauthenticator,enolfc/oauthenticator,NickolausDS/oauthenticator,santi81/oauthenticator,jupyter/oauthenticator,yuvipanda/mwoauthenticator,jupyter/oauthenticator,yuvipanda/mwoauthenticator,minrk/oauthenticator,jupyterhub/oauthenticator