Use CachedNetworkImage and separate cache for thumbnails on library page (#509)

* Use CachedNetworkImage and separate cache for thumbnails on library page

* Use caching for shared albums as well

* Introduce cache service

mobile/lib/shared/services/cache.service.dart

@@ -0,0 +1,21 @@
+import 'package:flutter_cache_manager/flutter_cache_manager.dart';
+import 'package:hooks_riverpod/hooks_riverpod.dart';
+
+enum CacheType {
+  albumThumbnail,
+  sharedAlbumThumbnail;
+}
+
+final cacheServiceProvider = Provider((_) => CacheService());
+
+class CacheService {
+
+  BaseCacheManager getCache(CacheType type) {
+    return _getDefaultCache(type.name);
+  }
+
+  BaseCacheManager _getDefaultCache(String cacheName) {
+    return CacheManager(Config(cacheName));
+  }
+
+}