Images in posts take up too much space

In a post, the images take up far too much space because they rely on `height` and `width` in the `img` tag. We need to find a way to class images so that they're centered horizontally (something like `margin: 0 auto;`) and size down at lower screen sizes without overflow their bounds.

No file or test is named. Start by locating the post image markup and the Sage theme styles; done means post images are centered, scale down at smaller screen sizes, and do not overflow their bounds.

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