CLC-3215: Allow deep linking into CalCentral

https://jira.ets.berkeley.edu/jira/browse/CLC-3215

Task: In order to support linking from Cal Student Central or Bear
Facts directly to My Academics or My Finances, we need to be able
to pass the correct URL to CalNet so that the user can go directly
to those pages in CalCentral.

Fix:
1. userService.signIn - capture the desired path on the client-side
2. SessionsController::new - Pass the "smart_path" parameter to our
   OmniAuth provider for CAS (/auth/cas?smart_path=<smart_path>)
3. SessionsController::continue_login_success - in the OmniAuth CAS
   callback, consider the smart_path parameter when making a successful
   authenticated redirect