Add ability to customize 'next' param in sign out url

We're using SSO and when a user signs out of User Echo, I need to redirect them to the signout URL of our SSO tool as well. Otherwise the following happens:

* User clicks 'Sign Out' link in User Echo

* They are signed out of User Echo and the 'next' portion of the logout link apparently directs their browser to try to reload the home page of the forum

* The user is no longer logged in to User Echo and so are (according to the SSO settings for my User Echo account) automatically redirected to our SSO login URL.

* The user is still logged in to our SSO site, and so they are immediately redirected back to the User Echo site with a new SSO token

* The user is signed back in to User Echo and the forum home page loads

Thus, the user gets the impression that nothing happens when they click the 'Sign Out' link.

If it was possible to customize the 'next' param of the logout link, I would simply redirect users to our SSO sign out link and all would be well.

Thanks for considering!