Adds semantic labels to images and modal close button (#56)

* Added semantic labels to images.

* Reverting project file.

* Semantic label for close button.

veggieseasons/lib/screens/details.dart

@@ -76,6 +76,7 @@ class DetailsScreen extends StatelessWidget {
             child: Image.asset(
               veggie.imageAssetPath,
               fit: BoxFit.cover,
+              semanticLabel: 'A background image of ${veggie.name}',
             ),
           ),
           Positioned(

veggieseasons/lib/widgets/close_button.dart

@@ -62,6 +62,7 @@ class _ColorChangingIconState
   Widget build(BuildContext context) {
     return Icon(
       widget.icon,
+      semanticLabel: 'Close button',
       size: widget.size,
       color: _colorTween?.evaluate(animation),
     );

veggieseasons/lib/widgets/veggie_card.dart

@@ -122,6 +122,7 @@ class VeggieCard extends StatelessWidget {
           Image.asset(
             veggie.imageAssetPath,
             fit: BoxFit.cover,
+            semanticLabel: 'A card background featuring ${veggie.name}',
           ),
           Positioned(
             bottom: 0.0,

veggieseasons/lib/widgets/veggie_headline.dart

@@ -49,6 +49,7 @@ class VeggieHeadline extends StatelessWidget {
               borderRadius: BorderRadius.circular(10.0),
               child: Image.asset(
                 veggie.imageAssetPath,
+                semanticLabel: 'An icon showing ${veggie.name}',
                 fit: BoxFit.fitWidth,
               ),
             ),