Make it easy to cache new data

lib/models/cache_model.dart

@@ -0,0 +1,19 @@
+import 'package:comunic/helpers/database/database_contract.dart';
+import 'package:meta/meta.dart';
+
+/// Cache base model
+///
+/// @author Pierre HUBERT
+
+abstract class CacheModel {
+  final int id;
+
+  const CacheModel({@required this.id}) : assert(id != null);
+
+  /// Initialize a CacheModel from a map
+  CacheModel.fromMap(Map<String, dynamic> map)
+      : id = map[BaseTableContract.C_ID];
+
+  /// Convert the object to a map
+  Map<String, dynamic> toMap();
+}