118 - Implement shared album feature (#124)

* New features 
  - Share album. Users can now create albums to share with existing people on the network.
  - Owner can delete the album.
  - Owner can invite the additional users to the album.
  - Shared users and the owner can add additional assets to the album.
* In the asset viewer, the user can swipe up to see detailed information and swip down to dismiss.
* Several UI enhancements.

mobile/lib/modules/sharing/models/asset_selection_state.model.dart

@@ -0,0 +1,103 @@
+import 'dart:convert';
+
+import 'package:collection/collection.dart';
+
+import 'package:immich_mobile/shared/models/immich_asset.model.dart';
+
+class AssetSelectionState {
+  final Set<String> selectedMonths;
+  final Set<ImmichAsset> selectedNewAssetsForAlbum;
+  final Set<ImmichAsset> selectedAdditionalAssetsForAlbum;
+  final Set<ImmichAsset> selectedAssetsInAlbumViewer;
+  final bool isMultiselectEnable;
+
+  /// Indicate the asset selection page is navigated from existing album
+  final bool isAlbumExist;
+  AssetSelectionState({
+    required this.selectedMonths,
+    required this.selectedNewAssetsForAlbum,
+    required this.selectedAdditionalAssetsForAlbum,
+    required this.selectedAssetsInAlbumViewer,
+    required this.isMultiselectEnable,
+    required this.isAlbumExist,
+  });
+
+  AssetSelectionState copyWith({
+    Set<String>? selectedMonths,
+    Set<ImmichAsset>? selectedNewAssetsForAlbum,
+    Set<ImmichAsset>? selectedAdditionalAssetsForAlbum,
+    Set<ImmichAsset>? selectedAssetsInAlbumViewer,
+    bool? isMultiselectEnable,
+    bool? isAlbumExist,
+  }) {
+    return AssetSelectionState(
+      selectedMonths: selectedMonths ?? this.selectedMonths,
+      selectedNewAssetsForAlbum: selectedNewAssetsForAlbum ?? this.selectedNewAssetsForAlbum,
+      selectedAdditionalAssetsForAlbum: selectedAdditionalAssetsForAlbum ?? this.selectedAdditionalAssetsForAlbum,
+      selectedAssetsInAlbumViewer: selectedAssetsInAlbumViewer ?? this.selectedAssetsInAlbumViewer,
+      isMultiselectEnable: isMultiselectEnable ?? this.isMultiselectEnable,
+      isAlbumExist: isAlbumExist ?? this.isAlbumExist,
+    );
+  }
+
+  Map<String, dynamic> toMap() {
+    final result = <String, dynamic>{};
+
+    result.addAll({'selectedMonths': selectedMonths.toList()});
+    result.addAll({'selectedNewAssetsForAlbum': selectedNewAssetsForAlbum.map((x) => x.toMap()).toList()});
+    result
+        .addAll({'selectedAdditionalAssetsForAlbum': selectedAdditionalAssetsForAlbum.map((x) => x.toMap()).toList()});
+    result.addAll({'selectedAssetsInAlbumViewer': selectedAssetsInAlbumViewer.map((x) => x.toMap()).toList()});
+    result.addAll({'isMultiselectEnable': isMultiselectEnable});
+    result.addAll({'isAlbumExist': isAlbumExist});
+
+    return result;
+  }
+
+  factory AssetSelectionState.fromMap(Map<String, dynamic> map) {
+    return AssetSelectionState(
+      selectedMonths: Set<String>.from(map['selectedMonths']),
+      selectedNewAssetsForAlbum:
+          Set<ImmichAsset>.from(map['selectedNewAssetsForAlbum']?.map((x) => ImmichAsset.fromMap(x))),
+      selectedAdditionalAssetsForAlbum:
+          Set<ImmichAsset>.from(map['selectedAdditionalAssetsForAlbum']?.map((x) => ImmichAsset.fromMap(x))),
+      selectedAssetsInAlbumViewer:
+          Set<ImmichAsset>.from(map['selectedAssetsInAlbumViewer']?.map((x) => ImmichAsset.fromMap(x))),
+      isMultiselectEnable: map['isMultiselectEnable'] ?? false,
+      isAlbumExist: map['isAlbumExist'] ?? false,
+    );
+  }
+
+  String toJson() => json.encode(toMap());
+
+  factory AssetSelectionState.fromJson(String source) => AssetSelectionState.fromMap(json.decode(source));
+
+  @override
+  String toString() {
+    return 'AssetSelectionState(selectedMonths: $selectedMonths, selectedNewAssetsForAlbum: $selectedNewAssetsForAlbum, selectedAdditionalAssetsForAlbum: $selectedAdditionalAssetsForAlbum, selectedAssetsInAlbumViewer: $selectedAssetsInAlbumViewer, isMultiselectEnable: $isMultiselectEnable, isAlbumExist: $isAlbumExist)';
+  }
+
+  @override
+  bool operator ==(Object other) {
+    if (identical(this, other)) return true;
+    final setEquals = const DeepCollectionEquality().equals;
+
+    return other is AssetSelectionState &&
+        setEquals(other.selectedMonths, selectedMonths) &&
+        setEquals(other.selectedNewAssetsForAlbum, selectedNewAssetsForAlbum) &&
+        setEquals(other.selectedAdditionalAssetsForAlbum, selectedAdditionalAssetsForAlbum) &&
+        setEquals(other.selectedAssetsInAlbumViewer, selectedAssetsInAlbumViewer) &&
+        other.isMultiselectEnable == isMultiselectEnable &&
+        other.isAlbumExist == isAlbumExist;
+  }
+
+  @override
+  int get hashCode {
+    return selectedMonths.hashCode ^
+        selectedNewAssetsForAlbum.hashCode ^
+        selectedAdditionalAssetsForAlbum.hashCode ^
+        selectedAssetsInAlbumViewer.hashCode ^
+        isMultiselectEnable.hashCode ^
+        isAlbumExist.hashCode;
+  }
+}