Studio: Fix - Forgot Password Modal (resolves STUD-689)

This work corrects the "forgot password" link on the Studio Sign In view to point to the login view (on the LMS side) which now consistently houses the Forgot Password modal UI (rather than the older homepage view that was replaced on edx.org some time ago). 

Resolves https://edx-wiki.atlassian.net/browse/STUD-689.