Added new query options for tags, added pdf preview on documents scanner page

lib/extensions/dart_extensions.dart

@@ -7,3 +7,18 @@ extension NullableMapKey<K, V> on Map<K, V> {
     return putIfAbsent(key, () => value);
   }
 }
+
+extension Unique<E, Id> on List<E> {
+  List<E> unique([Id Function(E element)? id, bool inplace = true]) {
+    final ids = <Id>{};
+    var list = inplace ? this : List<E>.from(this);
+    list.retainWhere((x) => ids.add(id != null ? id(x) : x as Id));
+    return list;
+  }
+}
+
+extension DuplicateCheckable<T> on Iterable<T> {
+  bool hasDuplicates() {
+    return toSet().length != length;
+  }
+}