Have heat map adjust its color range based on linear scale

static/js/directives/ui/heatmap.js

@@ -49,15 +49,30 @@ angular.module('quay').directive('heatmap', function () {
           });
         }
 
-        cal.update(formatData(data));
+        var formatted = formatData(data);
+        cal.update(formatted.data);
+        cal.setLegend(formatted.legendDomain);
       };
 
       var formatData = function(data) {
         var timestamps = {};
+        var max = 1;
         data.forEach(function(entry) {
           timestamps[moment(entry.date).unix()] = entry.count;
+          max = Math.max(max, entry.count);
         });
-        return timestamps;
+
+        var domain = [];
+        var current = 1;
+        for (var i = 0; i < 4; ++i) {
+          domain.push(current);
+          current += max / 5;
+        }
+
+        return {
+          data: timestamps,
+          legendDomain: domain
+        };
       };
 
       $scope.$watch('data', function() {