ECOM-574 Updated track selection page to be responsive

common/djangoapps/course_modes/views.py

common/static/js/spec_helpers/rwd_header_footer.js

lms/envs/common.py

lms/static/images/verified-ribbon.png

lms/static/sass/base/_grid-settings.scss

lms/static/sass/base/_variables.scss

lms/static/sass/shared/_footer.scss

lms/static/sass/shared/_header.scss

lms/static/sass/views/_verification.scss

lms/templates/main.html

lms/templates/navigation-edx.html

lms/templates/verify_student/_verification_header.html