#3192: Handle single logon link.
Fix merge conflicts.
#3192: Finish up login link to ready it for testing.
#3192: Redirecting to a site works. Don't know if logging in works.
#3192: Successfully log in user and redirect to a vsite.
#3192: Open cp/welcome overlay when user is redirected after creating a site.
Merge SCHOLAR-3.x into 3192-site_login_link
Merge SCHOLAR3.x into 3192-site_login_link
Merge branch 'SCHOLAR-3.x' into 3192-site_login_link
Merge pull request #3268 from openscholar/3192-site_login_link

Single-use login and redirect to site link