Add a key to the map

To help people understand that broadcasting is not a precise technology,
we have shown the estimate bleed area on the map.

Because people aren’t familiar with the technology a visual only clue is
not enough. So this commit adds a key to the map, which explains what
the different outlines mean.

It also removes the sticky footer from this page to:
- make the key visible on the page
- make people scroll and review the map before they get to the big green
  button
- not reduce the size of the map any further

app/templates/views/broadcast/partials/area-map-javascripts.html

@@ -5,10 +5,10 @@
   {% for polygon in broadcast_message.simple_polygons.bleed.as_coordinate_pairs_lat_long %}
     polygons.push(
       L.polygon({{polygon}}, {
-        opacity: 0.5,
-        color: '#2B8CC4', // $light-blue
-        fillColor: '#2B8CC4', // $light-blue
-        fillOpacity: 0.2,
+        opacity: 0.8,
+        color: '#005ea5', // $light-blue
+        fillColor: '#005ea5', // $light-blue
+        fillOpacity: 0.15,
         weight: 2
       })
     );
@@ -17,10 +17,10 @@
   {% for polygon in broadcast_message.simple_polygons.as_coordinate_pairs_lat_long %}
     polygons.push(
       L.polygon({{polygon}}, {
-        opacity: 0.1,
-        color: '#2B8CC4', // $black
-        fillColor: '#2B8CC4', // $light-blue
-        fillOpacity: 0.4,
+        opacity: 0.3,
+        color: '#005ea5', // $black
+        fillColor: '#005ea5', // $light-blue
+        fillOpacity: 0.3,
         weight: 1
       })
     );