Fixed image scaling in Digest mode and added inertial scrolling for iOS.

The first commit fixes an issue where in Digest mode images would only be scaled in one dimension (width) but not height. Height is now adjusted so images maintain their aspect ratios.

The second commit adds one line of CSS code for the feeds, headlines, and article sections in Digest mode to enable inertial scrolling for iOS devices. I'm not sure how you feel about adding browser-specific CSS, but inertial scrolling really improves usability and the required CSS is very minimal.

(I don't have an Android test/device to develop inertial scrolling on that platform; researching it led me to believe it requires a little more work (JavaScript library, etc.).)