UX-1642 Making visual tweaks and enhancements to the logistration form

common/test/acceptance/pages/lms/login_and_register.py

lms/static/js/spec/search/search_spec.js

lms/static/js/spec/student_account/login_spec.js

lms/static/js/spec/student_account/register_spec.js

lms/static/sass/views/_login-register.scss

lms/templates/student_account/form_field.underscore

openedx/core/djangoapps/user_api/tests/test_views.py

openedx/core/djangoapps/user_api/views.py