image modal should support ESC key and outer clicking to close the modal

[atlasgong]

Describe the bug
The image modal only closes when clicking the "X" button.

Expected behavior
It should close when pressing escape on a keyboard or when clicking outside the image.

To Reproduce
Steps to reproduce the behavior:

1. Go to any post with an image modal
2. Open the image
3. Escape, note that it doesn't close the modal
4. Click outside the image, note that it doesn't close the modal