Rename CSS classes for consistency

This prefixes everything to do with areas/the map with `area-list`, so
from looking at one element you know which `.scss` file will contain the
relevant code.

tests/app/main/views/test_broadcast.py

@@ -430,11 +430,11 @@ def test_preview_broadcast_areas_page(
         for item in page.select('ul.area-list li.area-list-item')
     ] == areas_listed
 
-    assert len(page.select('#map')) == 1
+    assert len(page.select('#area-list-map')) == 1
 
     assert [
         normalize_spaces(item.text)
-        for item in page.select('ul li.area-key')
+        for item in page.select('ul li.area-list-key')
     ] == estimates