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/views/asset_selection_page.dart

@@ -0,0 +1,95 @@
+import 'package:auto_route/auto_route.dart';
+import 'package:flutter/material.dart';
+import 'package:flutter_hooks/flutter_hooks.dart';
+import 'package:hooks_riverpod/hooks_riverpod.dart';
+import 'package:immich_mobile/modules/sharing/models/asset_selection_page_result.model.dart';
+import 'package:immich_mobile/modules/sharing/providers/asset_selection.provider.dart';
+import 'package:immich_mobile/modules/sharing/ui/asset_grid_by_month.dart';
+import 'package:immich_mobile/modules/sharing/ui/month_group_title.dart';
+import 'package:immich_mobile/shared/providers/asset.provider.dart';
+import 'package:immich_mobile/modules/home/ui/draggable_scrollbar.dart';
+
+class AssetSelectionPage extends HookConsumerWidget {
+  const AssetSelectionPage({Key? key}) : super(key: key);
+  @override
+  Widget build(BuildContext context, WidgetRef ref) {
+    ScrollController _scrollController = useScrollController();
+    var assetGroupMonthYear = ref.watch(assetGroupByMonthYearProvider);
+    final selectedAssets = ref.watch(assetSelectionProvider).selectedNewAssetsForAlbum;
+    final newAssetsForAlbum = ref.watch(assetSelectionProvider).selectedAdditionalAssetsForAlbum;
+    final isAlbumExist = ref.watch(assetSelectionProvider).isAlbumExist;
+
+    List<Widget> _imageGridGroup = [];
+
+    String _buildAssetCountText() {
+      if (isAlbumExist) {
+        return (selectedAssets.length + newAssetsForAlbum.length).toString();
+      } else {
+        return selectedAssets.length.toString();
+      }
+    }
+
+    Widget _buildBody() {
+      assetGroupMonthYear.forEach((monthYear, assetGroup) {
+        _imageGridGroup.add(MonthGroupTitle(month: monthYear, assetGroup: assetGroup));
+        _imageGridGroup.add(AssetGridByMonth(assetGroup: assetGroup));
+      });
+
+      return Stack(
+        children: [
+          DraggableScrollbar.semicircle(
+            backgroundColor: Theme.of(context).primaryColor,
+            controller: _scrollController,
+            heightScrollThumb: 48.0,
+            child: CustomScrollView(
+              controller: _scrollController,
+              slivers: [..._imageGridGroup],
+            ),
+          ),
+        ],
+      );
+    }
+
+    return Scaffold(
+      appBar: AppBar(
+        elevation: 0,
+        leading: IconButton(
+          icon: const Icon(Icons.close_rounded),
+          onPressed: () {
+            ref.watch(assetSelectionProvider.notifier).removeAll();
+            AutoRouter.of(context).pop(null);
+          },
+        ),
+        title: selectedAssets.isEmpty
+            ? const Text(
+                'Add photos',
+                style: TextStyle(fontSize: 18),
+              )
+            : Text(
+                _buildAssetCountText(),
+                style: const TextStyle(fontSize: 18),
+              ),
+        centerTitle: false,
+        actions: [
+          (!isAlbumExist && selectedAssets.isNotEmpty) || (isAlbumExist && newAssetsForAlbum.isNotEmpty)
+              ? TextButton(
+                  onPressed: () {
+                    var payload = AssetSelectionPageResult(
+                      isAlbumExist: isAlbumExist,
+                      selectedAdditionalAsset: newAssetsForAlbum,
+                      selectedNewAsset: selectedAssets,
+                    );
+                    AutoRouter.of(context).pop(payload);
+                  },
+                  child: const Text(
+                    "Add",
+                    style: TextStyle(fontWeight: FontWeight.bold),
+                  ),
+                )
+              : Container()
+        ],
+      ),
+      body: _buildBody(),
+    );
+  }
+}