Address site Accessibility Issues

[ronardcaktus]

This PR addresses several accessibility issues flagged by an external tool and reported to the client. The sites that have accessibility issues are listed in the issue, along with a PDF the client shared with us.

Note: While fixing these I noticed that the url health-alerts/ was pretty slow so I went ahead and optimized it.

Closes #320

[ronardcaktus]

Before Health Alert Query optimization

from django.test import RequestFactory
from apps.health_alerts.models import HealthAlertListPage

request = RequestFactory().get('/')
halp = HealthAlertListPage.objects.first()
halp.get_context(request)

context = halp.get_context(request)
context['health_alerts'].count()
443

After Health Alert Query optimization

context['health_alerts'].count()
Out[7]: 443

The same number of queries is being returned, showing that the optimization didn't seem to break anything.