Allow switching to next/previous image in image view

[rugk]

Expected Behavior

When viewing the image, let me click on the right/left site or an arrow to select the previous/next image in the chat.
Just how you can also do that in the media overview in the Android app.

Current Behavior

I have to close the image, search for the previous/next image in the chat and click on it again.

[dbrgn]

This is quite tricky because we don't know in advance what images there are (if they aren't loaded yet). In contrast to the app, we can't just query the database. Just considering images in the already loaded part of the conversation could be a partial solution to this.