JournalList: Implement Hero transition

This was especially challenging because of this bug -
https://github.com/flutter/flutter/issues/36220

It's why we need the extra flightShuttleBuilder

lib/screens/journal_browsing.dart

@@ -150,7 +150,7 @@ class NoteViewer extends StatelessWidget {
       padding: const EdgeInsets.all(16.0),
     );
 
-    return view;
+    return Hero(tag: note.filePath, child: view);
   }
 
   /*

lib/widgets/journal_list.dart

@@ -51,7 +51,16 @@ class JournalList extends StatelessWidget {
         var note = notes[i];
         return IconDismissable(
           key: ValueKey("JournalList_" + note.filePath),
+          child: Hero(
+            tag: note.filePath,
             child: _buildRow(context, note, i),
+            flightShuttleBuilder: (BuildContext flightContext,
+                    Animation<double> animation,
+                    HeroFlightDirection flightDirection,
+                    BuildContext fromHeroContext,
+                    BuildContext toHeroContext) =>
+                Material(child: toHeroContext.widget),
+          ),
           backgroundColor: Colors.red[800],
           iconData: Icons.delete,
           onDismissed: (direction) {