Accessibility tweaks for account settings and profile pages.

.../js/spec/student_account/account_settings_factory_spec.js

lms/static/js/spec/student_account/helpers.js

lms/static/js/spec/views/fields_helpers.js

lms/static/js/spec/views/fields_spec.js

...tatic/js/student_account/views/account_settings_fields.js

...tatic/js/student_profile/views/learner_profile_factory.js

...static/js/student_profile/views/learner_profile_fields.js

lms/static/js/views/fields.js

lms/static/sass/shared/_fields.scss

lms/templates/fields/field_dropdown.underscore

lms/templates/fields/field_readonly.underscore

lms/templates/fields/field_textarea.underscore

lms/templates/student_account/account_settings.html

lms/templates/student_profile/learner_profile.html