Adds veggieseasons preferences, tweaks styles + list page (#37)

veggieseasons/lib/screens/details.dart

@@ -9,13 +9,19 @@ import 'package:veggieseasons/data/model.dart';
 import 'package:veggieseasons/data/veggie.dart';
 import 'package:veggieseasons/styles.dart';
 
-/// A circular widget that indicates in which seasons a particular veggie can be
-/// harvested. It displays the first two letters of the season and uses a
-/// different background color to represent each of the seasons as well.
+/// A circular widget that represents a season of the year.
+///
+/// The season can be displayed as a valid harvest season or one during which a
+/// particular veggie cannot be harvested. Bright colors are used in the first
+/// case, and grays in the latter.
 class SeasonCircle extends StatelessWidget {
+  SeasonCircle(this.season, this.isHarvestTime);
+
+  /// Season to be displayed by this widget.
   final Season season;
 
-  SeasonCircle(this.season);
+  /// Whether or not [season] should be presented as a valid harvest season.
+  final bool isHarvestTime;
 
   String get _firstChars {
     return '${season.toString().substring(7, 8).toUpperCase()}'
@@ -28,7 +34,9 @@ class SeasonCircle extends StatelessWidget {
       padding: const EdgeInsets.all(4.0),
       child: DecoratedBox(
         decoration: BoxDecoration(
-          color: Styles.seasonColors[season],
+          color: isHarvestTime
+              ? Styles.seasonColors[season]
+              : Styles.transparentColor,
           borderRadius: BorderRadius.circular(25.0),
           border: Styles.seasonBorder,
         ),
@@ -36,7 +44,12 @@ class SeasonCircle extends StatelessWidget {
           height: 50.0,
           width: 50.0,
           child: Center(
-            child: Text(_firstChars, style: Styles.seasonText),
+            child: Text(
+              _firstChars,
+              style: isHarvestTime
+                  ? Styles.activeSeasonText
+                  : Styles.inactiveSeasonText,
+            ),
           ),
         ),
       ),
@@ -116,8 +129,9 @@ class DetailsScreen extends StatelessWidget {
             mainAxisSize: MainAxisSize.max,
             children: [
               Wrap(
-                children:
-                    veggie.seasons.map<Widget>((s) => SeasonCircle(s)).toList(),
+                children: Season.values.map((s) {
+                  return SeasonCircle(s, veggie.seasons.contains(s));
+                }).toList(),
               ),
               SizedBox(width: 8.0),
               Expanded(