Add / after teamsURL for Shibboleth redirect target.

teamsURL is defined without trailing /, so we need to append the
URL path at each use. This is done consistently throughout the
code, except on login. This causes a spurious redirect from
https://teams.example.org/teams -> https://teams.example.org/teams/
after login.
Merge pull request #7 from thijskh/master

Add / after teamsURL for Shibboleth redirect target.