feat: mark folders as read & GIFs section in saved messages [Android Contest]

[izadiegizabal]

I've implemented two new features that many users have requested. One of them is the possibility to mark all chats on a folder as read[1], and the other one to add the GIFs section to the saved messages chat[2].

These are the links to the request: [1] https://bugs.telegram.org/c/821 [2] https://bugs.telegram.org/c/720