Cancel signing in with OpenID = unmodified/unstyled generic template/page (BB-4798)

When you click an OpenID provider to sign in with from the Account -> OpenID section and then click "Cancel" on the provider page it returns to a generic template page located here:

https://bitbucket.org/account/openid/callback/?openid.mode=cancel&openid.ns=http%3A%2F%2Fspecs.openid.net%2Fauth%2F2.0

Tested using Google as the OpenID provider. I was already signed in to Google (so I just needed to confirm using my Google account as the OpenID provider) and I clicked "Cancel" to abort the process.