Max width doesn't suffice for tall images

[sk22]

The MAX_WIDTH defined in ImageAttachmentFrameLayout (as 400 dp) isn't ideal for determining whether an image should be displayed with full width or not, because it doesn't really help with very tall images (like screenshots). Maybe the image's aspect ratio is more suited for determining this? Or maybe there could be a maximum height for images, so tall images are displayed centered in cases where exceeded. This is an issue because, like in #166, possibly having to scroll down multiple screens because someone posted a very tall or narrow image imo isn't acceptable from an UX standpoint.