Restructure the public alerts page

.gitlab-ci.yml

config/settings/vm/base.py

gracedb/events/templatetags/mediaviews.py

gracedb/static/css/override-new.css

gracedb/superevents/templatetags/public_alerts.py

gracedb/superevents/urls.py

gracedb/superevents/views.py

gracedb/templates/alerts/index.html

gracedb/templates/base.html

gracedb/templates/gracedb/index.html

gracedb/templates/gracedb/manage_pipelines.html

gracedb/templates/navbar_frag.html

gracedb/templates/search/query.html

gracedb/templates/superevents/detail.html

gracedb/templates/superevents/public_alerts.html