Preview before sending images

[cstiens]

@n8fr8 Here's an idea for the UI to see the image before sending. Once the user taps send, we could show a progress spinner around the circle with an 'x' to cancel in the middle. The only thing this doesn't really solve is if someone sends a caption with the photo. Though, if they type a message with it and press send, it could go ahead and send both. I'll think on this a little more.