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/shared/ui/immich_loading_indicator.dart

@@ -0,0 +1,24 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_spinkit/flutter_spinkit.dart';
+
+class ImmichLoadingIndicator extends StatelessWidget {
+  const ImmichLoadingIndicator({
+    Key? key,
+  }) : super(key: key);
+
+  @override
+  Widget build(BuildContext context) {
+    return Container(
+      height: 60,
+      width: 60,
+      decoration: BoxDecoration(
+        color: Theme.of(context).primaryColor.withAlpha(200),
+        borderRadius: BorderRadius.circular(10),
+      ),
+      child: const SpinKitDancingSquare(
+        color: Colors.white,
+        size: 30.0,
+      ),
+    );
+  }
+}

mobile/lib/shared/ui/immich_sliver_persistent_app_bar_delegate.dart

@@ -0,0 +1,31 @@
+import 'dart:math';
+
+import 'package:flutter/material.dart';
+
+class ImmichSliverPersistentAppBarDelegate extends SliverPersistentHeaderDelegate {
+  final double minHeight;
+  final double maxHeight;
+  final Widget child;
+
+  ImmichSliverPersistentAppBarDelegate({
+    required this.minHeight,
+    required this.maxHeight,
+    required this.child,
+  });
+
+  @override
+  double get minExtent => minHeight;
+
+  @override
+  double get maxExtent => max(maxHeight, minHeight);
+
+  @override
+  Widget build(BuildContext context, double shrinkOffset, bool overlapsContent) {
+    return SizedBox.expand(child: child);
+  }
+
+  @override
+  bool shouldRebuild(ImmichSliverPersistentAppBarDelegate oldDelegate) {
+    return maxHeight != oldDelegate.maxHeight || minHeight != oldDelegate.minHeight || child != oldDelegate.child;
+  }
+}