add pages and level grouping for the browser

lib/src/models/kanji_item.dart

@@ -18,6 +18,7 @@ class SrsItem {
 
 class KanjiItem {
   final int id;
+  final int level;
   final String characters;
   final List<String> meanings;
   final List<String> onyomi;
@@ -26,6 +27,7 @@ class KanjiItem {
 
   KanjiItem({
     required this.id,
+    required this.level,
     required this.characters,
     required this.meanings,
     required this.onyomi,
@@ -35,6 +37,7 @@ class KanjiItem {
   factory KanjiItem.fromSubject(Map<String, dynamic> subj) {
     final int id = subj['id'] as int;
     final data = subj['data'] as Map<String, dynamic>;
+    final int level = data['level'] as int;
     final String characters = (data['characters'] ?? '') as String;
     final List<String> meanings = <String>[];
     final List<String> onyomi = <String>[];
@@ -60,6 +63,7 @@ class KanjiItem {
 
     return KanjiItem(
       id: id,
+      level: level,
       characters: characters,
       meanings: meanings,
       onyomi: onyomi,
@@ -105,6 +109,7 @@ class PronunciationAudio {
 
 class VocabularyItem {
   final int id;
+  final int level;
   final String characters;
   final List<String> meanings;
   final List<String> readings;
@@ -113,6 +118,7 @@ class VocabularyItem {
 
   VocabularyItem(
       {required this.id,
+      required this.level,
       required this.characters,
       required this.meanings,
       required this.readings,
@@ -121,6 +127,7 @@ class VocabularyItem {
   factory VocabularyItem.fromSubject(Map<String, dynamic> subj) {
     final int id = subj['id'] as int;
     final data = subj['data'] as Map<String, dynamic>;
+    final int level = data['level'] as int;
     final String characters = (data['characters'] ?? '') as String;
     final List<String> meanings = <String>[];
     final List<String> readings = <String>[];
@@ -155,6 +162,7 @@ class VocabularyItem {
 
     return VocabularyItem(
         id: id,
+        level: level,
         characters: characters,
         meanings: meanings,
         readings: readings,