Use custom marker icons for Favorite places and Visited places. (#31)

place_tracker/lib/place_map.dart

@@ -22,20 +22,17 @@ class PlaceMap extends StatefulWidget {
 class PlaceMapState extends State<PlaceMap> {
 
   static BitmapDescriptor _getPlaceMarkerIcon(PlaceCategory category) {
-    // TODO(kenzieschmoll): use custom marker assets.
-    double markerHue;
     switch (category) {
       case PlaceCategory.favorite:
-        markerHue = BitmapDescriptor.hueRed;
+        return BitmapDescriptor.fromAsset('assets/heart.png');
         break;
       case PlaceCategory.visited:
-        markerHue = BitmapDescriptor.hueViolet;
+        return BitmapDescriptor.fromAsset('assets/visited.png');
         break;
       case PlaceCategory.wantToGo:
       default:
-        markerHue = BitmapDescriptor.hueAzure;
+        return BitmapDescriptor.defaultMarker;
     }
-    return BitmapDescriptor.defaultMarkerWithHue(markerHue);
   }
 
   static List<Place> _getPlacesForCategory(PlaceCategory category, Map<Marker, Place> places) {

place_tracker/pubspec.yaml

@@ -22,5 +22,7 @@ dev_dependencies:
     sdk: flutter
 
 flutter:
+  assets:
+    - assets/
 
   uses-material-design: true